What makes you think, then that your SG will accept any of these enchantment ideas?
And that would be the critique of my own idea that I just thought of - again, pg. 121.
While it's been established that laboratory warp is not the same as regular Warp, there is no explicit guideline that says that (say) Vim magic can affect this new thing. So while the rules say that it's technically possible for a magic item to affect the laboratory Warp characteristic, it must have an effect that can do so. And by a strict reading of the RAW, there is no effect that would EXPLICITLY do so.
So if you really want to restrict it, there's your answer: lab warp is not explicitly covered by the guidelines, so therefore you can't design an effect that will affect laboratory warp.
However, to argue against myself (after I argued against myself) - that restriction seems unnecessarily tight, and seems to go against the general thrust of that chapter - for example, there are no explicit guidelines in the RAW (ie, nothing in the core rulebook in a callout box in the Magic chapter) for creating a lab Ignem bonus - but Covenents (pg. 122) gives examples for creating your own. Similarly, there are no guidelines for creating lab virtues - but the Covenents rules say that magic items can do so.
So it seems to suggest that magic items in labs can alter characteristics, even though there aren't any explicit guidelines in the core RAW that say "use this to modify lab characteristics" - in fact, that's kind of what the point of the rules on pg. 121-122 are there for.
As such, you really can't say that you can't modify lab warp because there aren't any core guidelines for it - there aren't any core guidelines for modifying ANY characteristics of a lab. You have to infer, based on the general descriptions of the characteristics themselves. If, say, having a permanent Ingem effect improves the Lighting quality and the study of Ignem, then is seems reasonable that a ReVi ward can shield the lab from extraneous vim effects.
But yeah - if your troupe doesn't want to let you reduce Warp, then that would be the argument they could use - although it's a bad one, IMO.
EDIT - even if that was the case, you could still argue for InVi monitoring equipment, and PeVi countermeasures, to enerally "identify and eliminate magical buildup" - even if you couldn't use ReVi or MuVi to control or modify it. The rules in Covenants seem to only require that you get something that reasonably MIGHT help with the characteristic, rather than requiring an explicit guideline.
"Tha RAW" wrt lab enchantments, which you quoted very selectively, is actually this:
(bolding and underscore mine)
So you see, that "tha RAW" entitles your SG to look up the phrase I underlined and thereby determine:
"Your enchantment removing a point of Warping Characteristics has powerful effects, influencing the whole of the lab, and thereby increases the Warping Characteristic again."
Showing you that Warping Characteristic is indeed very special, exactly where it relates to lab enchantments. 
Cheers
Sure, Covenants does, and magic items can be used in the lab, but they must have a Hermetic effect, which is based on a guideline, with R/D/T and other parameters for the effect, and uses per day, triggers, and other items for the item which is enchanted with the effect. As you say, no effect seems to do what is desired, and the example items in Covenants do one thing which is designed to aide in a small endeavor related to the lab work.
Again, what is the Hermetic effect that modifies lab warping? I can say that there aren't any core guidelines that does that. Are there effects that might possibly ameliorate the lab warping?
But yeah - if your troupe doesn't want to let you reduce Warp, then that would be the argument they could use - although it's a bad one, IMO. There are a lot of lab virtues that enhance warping, there are a few flaws that enhance warping. Virtues, by and large, IMO, are available at the discretion of the player. Flaws that have Warping can easily be removed by season's spent refining the lab.
The problem, in this specific instance isn't lab warping, it's a killer GM. There is no fix for this, except communicating with the GM, and if that prove unsuccessful just avoiding this particular trigger (see what I said about virtues and choice, and flaws and refinement). Saxonous has my sympathy in this regard. Opening up a dialogue about how lab warping is different from Warping due to powerful effects is important.
For what it's worth, I generally prefer the lab warping idea as a means of tracking warping of items that are under a constant and/or high level Hermetic effect. The idea of things getting warping points is interesting in theory, but in practice it's a huge mess for tracking what's going on with each individual item.
I knew there was something somewhere that linked both Warping. Thanks One Shot.
Reading between the lines of pp 121-2: if you use a shortcut with non-ritual spells to save yourself a season, you might pay for that season with Warping. Calling TANSTAAFL punitive is abusive.
Saxonous isn't asking for a free lunch. He's asking that his SG stop hitting him with excessively punitive effects for Lab Warping, which, reading between his lines, seems to be beyond what the RAW for Lab warping says. Unfortunately, that's beyond the scope of what is possible on a forum. The SG can easily ignore all of the recommendations made here. What needs to happen is that there needs to be some sort of consensus on what lab warping does in that troupe's saga, and then proceed from there.
A slightly warped lab isn't a big deal. Roll a simple die and if the result is less than the Warping score, then it has some side effect or modified effect. And for a Merinita, it's great if the warping aligns to the work being done, since it gets added to the lab total.
The best way to get rid of lab warping is to get rid of the source.
However it seems to me the better approach would be (for those playing as written) an enchantment to help ensure the warping effects were beneficial. Perhaps a ReVi or MuVi item that helps protect against malign influences, perhaps increases the warping score by another 1 but allows you to modify the roll for effects of warping or perhaps roll an extra die and choose between them...
Mr. Link has it in one. I would not mind the normal lab warping rules. Alas, what I get is "Your lab has a warping score, your items are warped in some way. And using the rules for a warped item seem dry, so I will pick what the flaw is, and you can find out what it is by experimenting with it in the field, or you can investigate it in the lab (using the normal"takes a season" rules, of course".
Alas, I have found with my STs, it's very hard to "push the donkey backwards", but pretty easy to "pull them along", so reducing the Warping Score, while actually reducing my personal power (The experimenting table is pretty nice, when actually used!), seems the best solution for this problem. Thus my request for ideas.
Items/spells that modify lab characteristics implicitly do NOT require a guideline, because no such guidelines exist to modify any of the 8 listed characteristics. If your SG required a guideline, it would render this section of Covenants null and void. Since the authors included these rules, they must be useable in some way, although THAT is subject to interpretation by your SG.
Also, the core book states that while "Powerful Effects" are subjective, it then goes on to list any Hermetic spell of sixth magnitude or higher as a powerful effect. As such, a level 20 effect that reduces lab warping by one fits all criteria, without automatically adding warping itself.
This is correct. The examples in the box on Covenants p.121 show, that there needs to be a negotiation with the troupe about the effects of a specific enchantment on the lab. There is no way around the troupe for this, unless you wish to stick very closely to the four examples in the box.
This is also the best advice I can give in case of cranky ArM5 SGs: involve the troupe. If, as Saxonous tells, his SG arbitrarily changes lab rules after the season, this should be talked over and adjudicated with the troupe asap. 'Ideas' from the forum used to "pull along" the SG tend to exasperate the issue, and the SG will quickly feel passed over.
Stirring ArM5 p.168 "powerful mystical effects" and Covenants p.121 "powerful effects" into a mulligan does not help a bit. Especially not, when you wish to keep a lab's Warping Characteristic apart from an effect's Warping.
Cheers
Yes. Which I acknowledged, here.
So you did not prove that a magic device is restricted from affecting warp in both directions. Therefore, the general RAW still stands.
That being said - as I said earlier, if your SG doesn't allow any sort of Vim effect to affect lab warp (despite there being no RAW guidelines for any characteristic modification), then yes - you're stuck.
Ah, so your SG is punitive. I can understand, I hate surprises. My sympathies.
I still believe using Refinement to remove unwanted Flaws might be the best way to reduce Warping. That and getting rid of Free Virtues.
Or you might make a second lab for your "safe" enchantments.