Sometimes you just have to forget who you are speaking to.
So: "MutoVim, guidelines", p159
Otherwise said "it is possible to use MutoVim to affect another spell before it has been cast."
Casting spells, under "formulaic magic" p81:
"If the casting totals equals or exceeds the level of the spell, the spell is cast and the maga suffers no ill effects. If the casting total falls short of the spell level by ten or less, the spell takes effect and the maga loses a Fatigue level. If the casting total falls short of the spell level by more than ten the spell fails to take effect, but the maga still loses a Fatigue level".
Casting spells, under "spontaneous magic" p81:
"spontaneous magic involves the production of effects which do not correspond to a spell the magus knows."
"Before casting the spell, the maga must decide on the effect she is trying to create."
"spell: an individual use of magic, generally Hermetic magic."
"formulaic magic: spells that have been worked out in detail ahead of time."
"spontaneous magic: Magic created by a magus on the spur of the moment, to meet an immediate need. Generally much weaker than Formulaic Magic, but much more flexible."
A spell is a single use of magic. It may be formulaic or spontaneous.
When a magus cast a spell, he brings that single use of magic in existence, ie, he does a magical effect.
Reading what I quoted about Muto vim: it is possible to use MutoVim to affect another thing (called incorrectly 'spell'), before even the moment we know if yes or now it will exist (which is the casting).
Hence it is not working on the product 'the spell' during the process 'the casting', because during the process, the spell doesn't exist.
The spell only exist when the casting succeed. If you are saying the opposite (a spell exist before the casting) then you are saying that you cast a spell wether or not you succeeded on the die roll, which contradict the rules.
Otherwise said (all trying to get you convinced):
Spell comes after a successful casting.
If you affect something during the casting, you can't be sure you affected a "spell", since suche spell could not appear if you fail the casting. Thus you are working on something else.
Thus, you are working on magic directly, which is totally correct since spells are individual uses of magic.
Thus, I used the words "magical energy forming the spell"
Which as for consequence that spell is the result of the casting, and MutoVim affect something during the casting, therefore,
- it doesn't need to have a duration (unless the special (and easily worked out) cases of ritual and ceremonial casting); which is something which render MutoVim useless.
- it doesn't have to have some penetration (other than the penetration required to beat the penetration of an uncooperative magus) to affect the target of the spell resulting from the casting; which is something which render MutoVim useless.
Hence: the rules were already more correct thant what the errate introduced, if you read them rightfully in the first place.
you want defecate on the roof of your wardrobe (which has magic resistance) rather than in your toilet. But you only have a spell called "defecate in my toilet". Solution? MutoVim your spell to turn you into a bird.
Defecating is the magical effect; your first range was "touch" (the toilet).
The turning in a bird is the MutoVim; you wanted to increase your range by something like a "Wizard's reach" spell to "voice" for example.
The result is as what you would have done without muto vim, but due to muto vim, you succeeeded at doing it on something which would have been otherwise unreachable.
Muto Vim all the way. Your excrement remain a magical effect, and your turning into bird doesn't need to penetrate any MR of your wardrobe.