It's a matter of interpretation. The base book has this:
THE LIMIT OF VIS
Hermetic magic cannot change the Art to
which raw vis is attuned. Most magi think that
this is a result of the Limit of Essential Nature.
Then AM has this:
If the magus wishes to break the Limit of Vis, it requires a Hermetic Breakthrough with 60 breakthrough points. [...] If this Breakthrough succeeds, then vis of any Art may be used for vis of any other Art.
So I think I understand your reading, but I think my reading where it says it breaks the limit of vis is probably valid too, because if you're not changing the vis itself, you might have found a corner exception but you haven't broken that limit. The example MuVi spell says: "The targeted spell, which would normally
use vis of any other type, may instead use vis of the specified Form."
You can read that to say you've made vis type irrelevant for the casting of the spell by changing the spell, but I think you can also read it to say you're changing the vis during the casting to adapt to the target spell. Mechanically speaking, in a momentary spell cast at the same time as the other spell, it doesn't matter. Muto Vim is typically restricted to the form if the spell, and in this case it's restricted by the form of vis despite the form of the spell. That the book talks of breaking the limit if vis is not hyperbolic for me - the vis is changed during the casting to adapt to the spell, even if the spell is the actual target. I would likely allow someone with the limit breaking breakthrough to change it with a non-mom duration, and as part of a lab action. The description is a one liner and therefore open to storyteller interpretation and player discussion. Whether you can then trade it on to the redcaps or not will vary from saga to saga.