True, but generally with other spells we can freely alter the parameters without needing a Breakthrough. Not being fully integrated, we cannot change those other parameters. We can only change the level and the size. So MuVi that changes things other than the R/D/T might work while MuVi that changes R/D/T does not work. That means finding MuVi that change non-R/D/T does not imply we can use MuVi to change R/D/T.
Also, WC doesn't work on AotH. You want Wizard's Vigil instead.
And a little addition: WC (or Vigil) functions w/ AotH just because both are pre-Hermetic, Mercurian stuff - both are partially integrated and understood. The only thing is sure about them is that they can be used together.
Wizard's Communion/Vigil works with all (non-spontaneous) spells using the Hermetic arts. Including poorly understood spells, partially integrated spells from whatever tradition, mystery spells, spells using unique parameters, etc.
They are all Hermetic spells.
@ErikT Yes, that is true.
What I wanted to emphasize is WHY Wiz.Comm. works w/ AotH
and WHY other spells do NOT work w/ AotH.
The question was about modifing AotH w/ MuVi or ReVi to give it Duration: Until.
Lots of spells can be used with/on the Aegis, but changing its parameters require a breakthrough.
Many other uses of Vim magic, such as suppressing it or dispelling it, works just fine on the Aegis.
Having an 'Until' duration Aegis is pretty awful, though. The Aegis has to change; to allow or disallow magi who move in or move away, apprentices, as Arts improve and greater castings are possible, and so on. True, it is not something that we can expect to be different every year, but it still ought to change more frequently than 'death of the magus'. Also -- would a Wizards Vigil casting of Aegis with an 'Until' duration disappear when any one of the casting magi died or went into twilight?
If you want to make the Aegis resistant to non-Ritual dispels, then there is no reason not to -- it can simply be a not-yet understood aspect of the non-Hermetic nature of the Aegis.
Sure, Until maybe wouldn't be your favorite, but imagine doing Aura. You can still dispel it but it lasts forever, and for a single casting. So now we have two options: Until v. Aura, depending on where you would prefer the risk.
Of course, one of the bigger problems with theoretically eternal AotH is change of membership/items.
"Until the membership of the mage council changes"
that should handle it.
I don't think you understood the point. Ending Until is easy. You could just have a secret code sentence or whatever. Similarly, you could dispel one with Aura Duration. The issue is that means you're going to recast them, just like you have to recast the Year one. How often does membership change or are items made? If it's often enough, then you're not gaining nearly so much using Until or Aura. The theoretically eternal AotH ends up being only desired in theory, not in practice.
Given that most magi live a century and a half or so, I'd figure the average duration of a member would be about 80 years. Six members being standard would mean the membership changes roughly every 12 to 14 years, so that's saving a fair amount of vis.
Notice the "item" bit I wrote as well. And then there are issues like Familiars.
True, but the mages might feel like those issues are worth the vis savings. For that matter its tough on any new covenfolk with supernatural abilities as well.
Or the risk of re-casting the Aegis. Let's not forget that:
a) Unless someone has mastered the ritual(s) involved, there's a serious botch risk involved.
b) Any interruption during the casting will interrupt the continuity of the Aegis protection, as the casting won't be resumed quickly enough.
In my sagas, these would be stronger incentives than vis-savings towards having an Aegis cast, let's say, every seven years or so rather than yearly.
Let me add that, as for making "native" to an Aegis new magi, familiars, grogs with supernatural abilities etc. the token is an easy solution. It is not viable for "imported" enchanted devices (note that those created inside the existing Aegis by "native" magi, including ones with a token, are treated as "native"), but ... is that really such a huge issue?
Hello, Vortigern.Sorry it took so long to reply.
As I quoted, you spoke of the importance of the Aegis in Maintaining the Pax Hermetica, which I took as implying it helps prevents conflicts between magi, an impression comforted by your later remark about how a PeVi specialist (thus, an hermetic mage) could dispel it.
And even then, you're probably right: without the aegis, an enemy maga might make magical attacks that would endanger a covenant's belongings and servants, and thus deprive her target's sodales of their magical power: You can't study properly if the servants who cook your food and clean your room are busy trying to kill your warring sodales.
As per the issue of the Aegis Duration, there's a simpler way, IMO, to get an "eternal" Aegis: Invent one with D: Conc (which already requires a major breakthrough), and then use a Revi effect cast by an item with constant duration. As noted by others, this would bring its own host of issues, as such an Aegis would be unchanging and unable to adapt 
The real issue with an until duration is that it gives your enemies the opportunity to satisfy the condition. Until the membership of the council changes. Wizard war and off a member, or simply persuade another covenant to make them a very lucrative offer to move to another covenant. Then the shield has fallen and you have an opportunity to... do whatever you would do to a covenant with no aegis.
Benefits of Until Duration
1 - Resistance to dispelling
2 - Until "I wish it to end" can last for years saving quite a bit of vis
3 - Reduces the risks of warping/twilight as it reduces the number of castings
4 - Allows multi Aegis to exist as typically the year duration ends at Solstice/Equinox which means you need to cast it on one of those days for it to be active for the year, limiting the number of Aegis magi can fully sustain
5 - You can protect more difficult to access locations or simply mundane allies locations
6 - You don't have to worry about travelling members of the convenant or those in Twilight or simply not available yearly for whatever reason
I also think per core rules, that non-Merinita magi also have access to a vanilla Until duration @ a +1 magnitude. In this case, the MuVi spell 'Boosts' the duration to Until... Could be free or ask the MuVi to have a +1 Penalty for complexity or use the /2 guideline or require a minor breakthrough (Until duration for non-Merinita) or a major breakthrough (AoTE parameter change via MuVi). All depending on how your saga wants to make it accessible.
As the default setting is that almost all convenant have an Aegis, I see most of them to be basic level 20 ones as you need ressources, Lab total to learn, Penetration, Seasons to learn / Master the new spell (unless you are Mercurian and have access to the special mastery) & convenant needs to also have enough Wizard Vigil levels. All of these low level Aegis are very fragile vs PeVi formulaic non-ritual magics. Only a small fraction of the order will have an Aegis that can hold its ground vs a Convenant vs Convenant wizard war and I think that is where the base paradigm of Arsmagica lies.
Having all convenant benefiting from an Until Aegis is not interesting
Corebook p.69 - "The number of Hermetic covenants with no Aegis at all can most likely be counted on the fingers of one hand, and most covenants want to have the strongest Aegis that they can manage."
Corebook p.112 - "Year: The spell lasts until sunrise on the fourth equinox or solstice after its casting. A spell with this duration must be ritual."
W
The whole thing about until duration, is it is Merinta. It's fae, it's about the story. Until midnight in Cinderalla. Until true love's first kiss in Snow White (and Shrek).
Until should have a story. Until I wish it to end require a very generous SG, or a power gaming group.
Usual caveat - If that works for you, great, however, general case, I consider Until duration should be carefully SG controlled.
If there's an Until Aegis (or any other spell), can InVi effects identify the condition? If so, what level?
If that's something enemies can divine, it's a much more dangerous option.
As SG in my campaigns, I'm much more story based than as per rules.
All Merinita magic compels the fey in some way. As for the other realms dabbling into the until duration, I've introduced an internal one which works nicely.
Divine I've never seen in play but until God no longer wills it seems interesting.
For the magic Realm, I'd personally require a form of Theurge magic to compel a magical entity to sponsor the effect.
W
I'd say if you can beat the spell level in a seasonal lab activity of InVi and used the object investigation rules, that would work.
Also, InMe in the head of those that know or Scrying as the effect is cast would work too.
If it is Merinita, then you can maybe make a deal with a fey. If infernal, a demon. If divine a prayer.
W