Would you agree to re-phrase as "lead the hunt?" Really all that could be enforced is that the parens has to participate, but the flavor is that the parens is the one with the most obligation of vengeance.
Here is a big loophole that I always thought should be in the Code, but never has been:
"I will not reveal the secret of Parma Magica to anyone outside the Order."
I would think, especially considering that Parma Magica actually works now (in 5th Edition rules), this would be a Big Deal -- especially for the Founders.
i like how 'just' sounds, but on the other hand, i don't like adding qualifiers. 
i do believe something about parma might fit. i think you should get marched for sharing that.
i don't think a magus should be marched for learning something about another magus by mundane means.
I think it's the rare magus who ~does~ agree they should be marched for anything they do. 
But remember, you can't afford to outline what is and is not "marchable", just things that are obviously and paramountly (?) so.
Worried about the spying thing, too. It takes away a lot of potential flavor and fun to the game.
Sure, magi are secretive, but they are also curious, so I don't think a decision to suppress any spying would be so popular, especially as there are antagonism between both maguses and covenants, whatever their house. Don't you think a traditionnalist covenant won't be interested in spying a transitionnalist one, and vice-versa? Think again. Same goes for the wilderists, crusading magi...
IMO, the provision against magical spying is there just to quiet things a little, just like you could say "Ok, no weapons, fists only".
Running short on time so this may have been addresses and I missed it but I wanted to get my thought down...
"Too bad for them." I'm guessing you dont play anyone from the listed houses. With that addition you may as well have the tyatlus chapter re-witten.
I think most magi would love having the loophole open. You want to declare wizards war. How do you find information about the target? Yes you could declare and then waste the month hoping you get lucky. Or you could prepare before hand by sending in a mundane spy to aquire ACs and learn the targets routine, and posible places of safety.
Your a great Bonisagus. You beleive that someone has stolen some of your work but have no proof. The queasitor will be a bit unhappy if you bother him with an unfounded theory. So instead you hire a mundae to get the info required which can then be presented to a queasator who, having some bit of proof, will investigate.
I'm sure there are several other senarios that given a moments though we can come up with. Mundane spying/theft ect.. has it's uses. the magi can easily defeat them if he wishes. Not a large enough threat to be included in the code, and make it a high crime
Senario #1:
you notice that your sodales has been acting funny lately. The addition of horns growing on his head and the odd color change to his eyes doesn't add to his 'warm fuzzy' demeanor. what do you do?
-
do nothing, and hope you don't die as he summons a greater deamon into the covenant.
-
call in a queasatorial investigation, only to discover that your sodales has somehow become part fae. he doesn't like the intrusion into his affairs, and retaliates by accusing you of srying. (for the sake of making my point) you get marched.
Senario #2:
your grogs come and inform you that there is a magus hanging out in the woods on the covenant lands, and he has been there for a few days. what do you do?
-
do nothing, for you do not wish to pry into his affairs.
-
do something (either confronting the magus and asking what he is doing on your land or telling your grogs to keep an eye on him) and chance getting marched for protecting your lands?
Senario #3:
over the course of a few months, you have noticed that your grogs have been showing less and less respect to you. when you finally confront a grog, he says "it's that bloody rat, master agnar," your sodales. how can you handle this if you can't 'pry into his affairs?'
Also, somewhere(?) I posted a thread asking re what constitutes a breach of the Code as written, whether "intent" is necessary, or just the spell.
While interpretations varied somewhat, one thing is clear - a spell, "magic", is verifiable. It either is, or isn't there.
If mundane "prying" was banned, then many magi would be loathe to so much as visit others, for once within the other's stomping grounds it would be all too easy to orchestrate "just cause" for a war, or for a surprise attack "in self defense". (Perhaps later adjudicated to be a crime, perhaps not, but of little comfort to the recently deceased either way.)
Talk about "looking at someone the wrong way"! 
Now we are getting into questions of interpretation of the Code and the level of compliance/enforcement in your game; we are outside the realm where one person's answer is "right" and another's is "wrong."
There is no law that can provide blanket justice without human decision-making getting involved. You've posited a scenario that could play out either way but it not necessarily incompatible with a provision against "prying." The investigating magus has a good reason for checking into his sodalis' activities: a suspicion the Code has been broken,
In my Saga what would likely happen is you would go ahead and investigate. The pointy-headed magus would take umbrage at the investigation and would have recourse to certamen to get your nose out of his business or Wizard's War to really get your nose out of his business. Let's assume he does neither because he doesn't expect to win. Instead he complains to the Quaesitores you've broken the Code. You counter-claim he's dealing with demons. Now you have a Hermetic investigation/trial on your hands. If the authorities do their jobs right, no one gets punished; the suspicious magus wasn't doing anything wrong, but the investigating magus had no way to know that and had reasonable suspicion of diabolism. Therefore (if there is any justice) forfeit immunity is a plausible defense.
If it's affecting your grogs, then it's your affair, not just his. I guess it's in the (Peripheral Code) definition of "prying." If you are directly affected by another magus's behavior then I submit it's not prying. So you ask your grogs what is going on and then use certamen or Wizard's War to make him stop. I don't see the problem here.
So if it is OK to hire mundanes to spy on another magus, I guess it's also OK to hire mundane to assassinate another magus. After all, I didn't kill or attempt to kill that magus. A mundane did. There's nothing in the Code that says you can't do that. You could even have a mundane act as your middleman with a demon.
Edit: OK, maybe that came out sounding more testy that I meant it to. I'm just surprised that other people seem to like the idea of magi using mundane pawns to get around the Code. It seems very contrary to the spirit of the Oath of brotherhood and everlasting loyalty.
I've never seen as so overly unbalanced. After all, any mage/covenant worth their salt would have more than a few defenses against mundane infiltration of this sort.
I've always had the impression that the practical goal of The Code was not to create some grand brotherhood (altho' certainly so in theory), so much as to get the various magi to stop blowing each other up long enough to lay a groundwork for that, a process that continues til the present year. And to achieve such, some allowances for conflict and options for pursuit of "non-brotherly activities" had to be made, just to find a middle ground, a starting point for all concerned.
Remember, the magi of "today" are not the ones whom that Code was originally addressing. What we're dealing with in The Code is not the best of all possible worlds, but the legacy of a very bellicose, antagonistic and aggressively competitive environment, involving a highly disparate group of (largely) xenophobic social cripples, and the best-result of putting the fires out (or at least carving a fire break). Any multi-national organization that meets only once every 7 years to discuss mutual business is not very hugs-and-bunnies oriented (much less every 49 years.)
And while some may see that as good cause for a rewriting, others will see any rewriting as a threat to the power base that they've built on the Code as it stands.
Now, since the premise in this thread is a rewriting of that document, we have the luxury to idealize both the legacy and the present state of affairs. I think that, were it put to a vote in a Grand Tribunal, more than a few agenda-minded magi would be happy to maintain a current status quo, if not a majority of them.
i'm just trying to show how impossible it is to not pry into the affairs of your sodales. in any of the senarios i posted, i believe the 'you' could get accused at tribunal of scrying. how can you suspect a fellow sodales of infernal tendancies if you did not have at least some idea as to what he was doing. (he was growing horns. if you weren't so noisy, you wouldn't know that) how did you know that the magus was in your woods? were you scrying on him? assuming that all injusticies will be covered in the peripherial code doesn't work for me. i agree with Cuchulainshound though. if i were a magus with this as part of the code, i would find my little hiding spot and never leave it for fear i would end up glancing in the wrong direction.
things might not start out as bad as that, but it can escalate. before you know it, someone will sue mcdonald's for not telling them that the hot coffee they bought was hot!
Well, IIRC there are rulings in the peripheral code (or was it only in 4th edition grimoire? - serf's parma...) stating that a mundane thief sent to another convent is not a violation to the code unless you give him some magical means like invisability.
And interaction trough mundanes to do things otherwise forbidden is what a lot of magi are doing all the time. Verditi magi imploy merchants (venditors) to sell magical items to mundanes; many convents use tame noblemen/noblewomen to interact with mundanes and those do meddle with their affairs.
If mundane spying was a capital offence, no quesitor would be able to seach a suspect's sanctum. Momentarily he still forfeits his immunity upon entering the other's sanctum but he is not breaking the code. By the way if mundane scying were forbidden you could slay any person having the bad luck to pass your sactum's door when you leave it as he might have gotten a glimpse of the interior...
I agree with Cuchulainshound that the Code should be a set of loose "big picture" principles. So I would like to take a different angle on the mundane/magical spying question and ask what is the operating principle here?
I do not think it is a threat to any magus if you want to find out his mailing address so you can send him flowers on his birthday. It is more of a threat if you try to follow his movements to find out where his vis sources are, or find out when he has left his sanctum so you can break in while he's gone. Or sell that information to another magus who is willing to pay you for it (and use it for nefarious purposes).
I think the principle in the Code should be that magi should have privacy of their magical resources (i.e. vis), spells, Arts, lab projects, etc. To me, whether someone finds all that out by magical or mundane means does not change the level of threat.
(Scrying deserves to be a special case IMO because it just makes it too easy to lay an ambush etc.)
I am sure there are different principles others would advance; what are they?
I am not sure I agree with that; really it depends on a definition of "prying," much as the "interference with mundanes" clause depends on a definition of "interference." If you have a reasonable standard for what constitutes "prying" then it does not have to be hard to live under this rule.
I do agree with you in that I do not see the Order as a rule-driven organization. Certainly not at the nitpicky level of splitting hairs over whether peeking into an open sanctum door is capital offense. I think a reasonable standard would be, how much effort did the magus go to to get the information and how valuable did the information prove to be?
By that standard, hiring a mundane spy to sneak into someone's covenant is a lot worse than accidentally casting an Intellego spell on an area where a magus happened to be. Let me ask you this: if you were a magus, which would offend you more?
Ok, trying to address as many as I can of the issues discussed in the last few days...
Re: the no-vendetta and vote prudently clausles of the Code, I'm really torn because I can see good points both for removing and for keeping them. In the end, the empasse must be broken, and I hope the best way is to to default on the canon, even if personally I deem them an unenforceable waste of ink. I hope that keeping it really improves the style, as several seem to think.
Re: the qualifier for a certamen. I do think it would be best to have one, if nothing else because the history of the Order clearly shows the dangers of letting it to have too much legal latitude (cfr. the failed Tremere coup). "Just" seems sufficiently good, wording-wise.
Re: the definition for protected renewable magic resources. I think we may all easily agree it is meant to cover auras and sources of vis, both magic and faerie. About what might be the most poetic, in-period definition, I am truly at a loss. The best I've come up with is a choice between "sources of magic" or "well-springs of magic". Paradoxically, if we forsake poetic, we might as well go for maximum clarity. After all, auras and vis are in-character terms, too. Why not speak of "magical auras" or "places of magic", and "sources of vis" or "sources of magical might" ? Again, I'm an analyst, not a poet.
Re: interfering in mundanes' affairs and molesting faerie/magical creatures. I share YR7' s argument about why "meddle" is better than "interfere" and "thereby" is better than "lest".
Re: the hunting rogue apprentices bit. Do you think "I will strike them with all my heart, lest their infractions tarnish myself" might be acceptable ? I think the spirit of the provision should be that the master must cooperate to the hunt at the best of his capabilities, but suggesting in any way that the master should be the first or the leader of the hunt IMO creates an unenforceable duty that might be abused. Punishing rogues ought to be and is best dealt with as a collective responsibility of the whole Order. The former master should be obliged to take part only insofar as he is actually useful.
Re: putting the Oath at the start or at the end of apprenticeship. IIRC, a slight majority of people prefer to leave the canon be. The argument for either way look convincing. If nobody has a really good argument, let the canon be. My own pet peeve on apprentices was to close the loophole that allowed to steal apprentices that are opened late to the Arts, but I'm coming to realize this may be a matter for the Peripheral Code.
Re: the prohibition on serving mundanes. I think it works best if put in the main Code, as I see this as much of a High Crime as molesting faeries or scrying sodales. It works as a nice balance, if at the same time you relax the prohibitions against interfering in mundane affairs.
Re: the Parma Magica. Oops. How I could have forgotten this ? 
This is stuff that really belongs in the main Code, now that the Order has relaxed his "join or die" policy on hedge wizards. I would only rephrase it to encompass all the secrets of Hermetic magic, not just the Parma. I would put a "I will not reveal nor attempt to reveal the secrets of Hermetic magic to anyone outside the Order", in the first paragraph of the Code. This is stuff that threatens the existence of the Order, like slaying wizards, harming the Gift, or destroying sources of vis/auras.
Re: the investigative powers of quaesitors. Trying to make the provision look less like legal slang, what about "I understand that should I break my Oath, this Code will not shield my crimes, and members of the Order shall inquire into my affairs and deliver their judgement. I will not presume to be inquisitor or judge of my sodales without the blessing of Tribunal, nor I will invade their mind, lest I turn justice into tyranny. "
I think the caveat about mind-reading should stand, both for in-character reasons, and because it makes for better stories, if Quaesitors cannot solve every case with a quick mind scan.
Re: the mundane vs. magical means of spying, I happen to share SirGarlon's arguments wholeheartedly. It seems to me that most mages would be more eager to get privacy about their magical secrets, and have them protected against mundane spying, rather than be allowed to spy others at leisure, if spells are out. IMO it is simply that in the Founders' time, the Order was far less crowded, and spread thinly on the land, so mundane means were not so practical for spying as they are now. The reasons why most mages would prefer to be protected from spies than to be a spy are as valid today as they were for the Founders, but now mudane spying is a better tool. Hence the interest in closing to loophole.
Re Tytalus magi, I absolutely do not want to be disrespectful to players of Tytali (heck, they are one of my preferred Houses ever). But I do not think they would have the political clout to have their viewpoint followed on this (they are one of the less numerous and popular houses, thanks to the lingering effects of the diabolist scandal), and I'm strongly persuaded that they are very very interesting character concept to play even if they are forced to be somewhat more circumspect on their spying of fellow mages. They can vent their urge to compete in so many directions besides spying. What I expect is that they will skirt the edges of the prohibition a lot, sometimes breach it utterly, and they will get a lot of convictions if and when they are caught, which won't be too often, since they are usually very good at their game. If they are caught, in all likelihood, they will get fines, not be Marched, since this is not a crime that threatens the survival of the Order or fellow magi. The only very rare Tytali will be Marched that is suicidally obdurate in claiming his right to spy magi by mundane tricks in the face of a Tribunal.
A tentative idea: Would it be a reasonable compromise and work better if we keep closing the mundane loophole but change the provision to: "nor I will pry into their secrets" ?
(A low point in American jurisprudence.) 
Imo, the real question is: Is it a violation to use magic to get the prospective thief to be gullible enough to try in the first place?! 
I think the very arrogance and elitism that has been previously mentioned is the difference; that, as a policy, the Order would view magical surveillance as innately far superior to anything mundane, and therefor by definition far, far more threatening.
(And it is, practically speaking. If a mage were to detect an undefined Scry, they might legitimately feel they need to immediately defend themselves, with legitimately excessive force against the unknown scryer. If they detect a mundane spy, a much less forceful response would be called for, and one not directly targeting a Hermetic member.)
(An overly strict interpretation might even rule that sending peasants to certain death (at least once it becomes obvious that will be the result), is a minor crime, tho' that might be a stretch.)
I think you're looking at the glass half-full. Unfortunately, as Skri' suggested (quoted at top), the issue does not depend on what is defined as illegal, but what can be stretched to be an excuse to take action while pointing to the Code as a mantle of justification for whatever action against those mundanes suited the acting mage. A mage either casts a spell, or they don't. ~IF they do, then the wheels could start turning, one way or another. But "mundane surveillance" is just too easy to (mis)interpret, and since killing a mundane or grog is barely a low crime, with such a flimsy excuse ready-made it could be an invitation for cold wars, which in turn could then escalate one way or another into something truly undesirable. At worst, widespread isolationism, a death knell for the Order.
Or, look at it the other way. As currently allowed, how many magi would start a mundane surveillance project? A few, some small percentage? And the fallout, if the act is both legal and detected? Again, it would be mundane, a (relatively) proportional and mundanely equivalent response of the same (mundane) caliber.
Otoh, how many magi would use this clause as an excuse to retaliate for some imaginary wrong? How many interpretation cases would a Tribunal see every year? And what are the larger ramifications of each action, re stability and functioning of the Order, and the mingling of magi?
It's not a question of which is theoretically desirable, but which, practically speaking, is less likely to be abused and do more harm than good.
Frankly given the power at the disposal of most mages, I would think that any mage/covenant which discovered a mundae spy would simply apply a bit of PeMe and voila, whatever he came to find out about, he doesnt know anymore.
Or if one is feeling particularly affronted, just take it a bit further and wipe his mind clean completely or drive him mad as a warning to any other mundanes foolish enough to sign up for the job of replacing him/her.
An apprentice has no rights, and is immune to any hermetic laws. If they do something in violation of the code it falls back on their master who should have trained them otherwise and can punish them appropriately. They also have no protection from the code and anything can be done to them, their only protection is what their master gives.
RE Apprentices: I agree with Agnar. Placing provisions in the Code about apprentices beyond current elevates their status to nearly that of Magi... which at current it is anything but. If that is your intent, OK. However at current they are more an item of property under the code rather than a protected person like a Magi. I, being a relatively conservative interpreter of the Code, favor the property approach to all mundane (including apprentices) affiliates of Magi. This makes it at best (or worst depending on perspective) a low crime to in any way harm/malign them. (Save perhaps a near gauntlet apprentice, which could then perhaps be deemed a magical resource. ) Which, rightly, reflects all such individual's lower status than Magi.
RE Wizard's War: The clause about no retribution I've always interpreted as meaning that there can be no -legal- retributions on the declarer of a war. This I think is important to have in the Code.
RE Mundane Spying: I think both that Magi are unlikely to consider this a real threat sufficient to include in the Code and that the effects of such a provision in the Code would be more negative than positive. Remember that we are dealing with a medieval political model. People expect there to be dealings and political maneuvering surrounding just about -every- vote cast. (Prudent, gentlemen?) This reminds me of the old quandary about casting an area intellego spell and 'accidentally' catching another mage in the area. According to the Code this obviously is a crime, though perhaps not a very serious one. Follow this line of logic through to applying it to mundane means of gathering information and the possibilities for trouble magnify greatly. The circumspectness required in judicious use of intellego now must be applied to mundane affairs. Virtual isolation is the only logical outcome.
Say for instance I desired have some manner of interaction with a given Mercantile Guild in a given city. How can I be -certain- that no other Mage has some manner of hidden dealings with said Guild? They are entitled to privacy in their dealings. If I initiate anything with said guild, unknowing their involvement, I'd very rapidly be guilty of unintentionally prying into their affairs. Which would potentially lead to an IC situation where both Magi discover each other's involvements and both identically suspicious of the other, accuse one another of prying into their affairs.
It is -much- too broad and flexible of a ban to enforce, with far too far reaching of negative consequences in my opinion.
RE: Parma / Secrets of Hermetic Magic: This falls directly under 'Join or Die'. A mage is free to teach whomever they wish. This person is then considered their apprentice. The caveat is that they are then expected to gauntlet and induct such individuals into the Order. Any mage who doesn't do so has gone renegade, and any apprentice that doesn't do so has chosen 'die'. All magic/magi of sufficient power to be 'relevant' are claimed by the Order, willingly or not. Much like Venice and rival glass makers, the Order ensures that a (relatively) peaceful society by/for Magi exists under it's banner because it doesn't allow anything else potentially rivalling to exist.
Re: Quaesitori: I'm not in favor of enshrining investigative powers in the Code. The idea of forfieture of immunity is enough for me. It also lends -far- more drama to investigative plotlines. Magic investigation is both rightly feared and forbidden, and... too far reaching and effective. Remember that Guernicus and other Qs are all just Magi themselves with allies/enemies etc. All magi would fear that the pet Qs of their local tribunal faction in power would come calling to 'investigate' something trumped up with the real goal of divining their secrets. A universal 'Over my dead body' would be my anticipated reaction.