I thought for sure this one would be in the forum archives, but I either missed it or it hasn't been asked in a lonnng time:
Can Creo be used to permanently grow someone's hair, nails, and the like? Someone living - obviously, one can create massive quantities of dead animal/human products with vis. I mean more, if a maga wanted to grow her hair out in a span of moments, or if a magus wanted a really rockin' beard.
Or is it a temporary Muto change?
A bit frivolous, I know, but it's something that would reasonably come up I think.
I would think this is similar to bringing a plant or animal to maturity. That is, it's not some sort of temporary Muto thing but a way of forcing things to progress naturally but more rapidly. Of course, you could use Muto, too. I won't be looking up the Herbam stuff until the morning at earliest, though.
If used to simply grow existing hair/nails longer, it's pretty straightforward. Creo is used to create stuff and to make something a "better" example of its type. So Creo would work for any of hair, beard, nails, etc.
The question would be what Technique could, for instance, create hair on a bald person, or grow a beard on a youth who has no facial hair, or on a woman. I think that would be more in the direction of "essential nature" (if not full such), and so require Muto.
However, to permanently restore hair growth on a man who has gone bald might be Creo - it has a feel of "healing" a problem, sim to if a burn caused hair loss - it's healing the damage and returning it to normal. Otoh, it is a natural change, and so a Flaw of old age, which might require Muto. Similarly with someone who, for instance, has white hair from a lightning strike - is it a "healing" thing, or a counter-natural change? Dealer's choice on that one.
In my opinion the closest guideline in the Art of Herbam would not be the Creo one about bringing a plant to full maturity (which already has an explicit Corpus counterpart), but the Rego Herbam Level 15 guideline "make a tree blossom out of season, in a moment". Of course, for magical, non-permanent hair growth, completely altering your appearing is a base effect of only Level 3...
That would be more approp if used to grow hair on a child where it had none yet, not to grow hair where it had naturally failed and would never grow again. If a plant only blossoms when young, Rego would not then cause it to blossom once past its age.
This is not a question of losing hair "out of season", as if an animal shedding a heavy winter coat (which Rego could control/counter), but of a loss more similar to a loss of a limb (which humans, unlike plants, do not grow back).