I think your looking at two different levels. what i will refer to as mutations and permanent alterations.
Mutations, are an instantaneous affect that through damage alters a part of the persons body these should be fairly simple, relatively permanent on a human, and are in the grey area. Examples would include
Fatter curse the person in such a way that they dont absorb nutrients properly, thus they grow fatter.
Complexity ~6 to beat there defense roll, +x to cause a consequence which will be the spells duration.
Skinnier As above
New face This will *not* be pretty. you'd be looking at things along the lines of breaking there nose, useing blunt trauma to reshape the skull ect., you'll need an extreme consequence.
New fingerprints Easiest to simply remove them entirely via fire.
New hair You could probably cause it to grow more or less, or make it white, anything more is verry probably a law violation.
Permanent Alterations
12 complexity to go from the standard thaumaturgical starting point of a day to a mortal lifetime. So thats your minimum. You will need another 30 to ensure it works, as all of these require extensive reworking of a persons body and thus invoke the section in your world that says that altering another person is the same thing as killing and remaking them.
Where exactly does it state in the book or novels that the person being willing makes it non lawbreaker?
The whole 'free will' thing. You can talk to the willing dead (ectomancy) but not make them do anything (necromancy). You can't break into their minds (Molly, for example), but you can go in and look if given permission Turn Coat Spoilers (Gatekeeper and Listens to the Wind in Turn Coat)
Furthermore, this isn't turning them into a newt, and destroying their minds with the shock and instant brain-size change. This is changing their appearance. While it is an important part of your self-image, it doesn't change your body in those importantly dangerous ways that full Transformation would.