Except Arya's House Rule 1 says that "Spontaneous Magic uses Intelligence rather than Stamina." But since Hiems's Sta and Int are the same, it doesn't really make a difference.
Muto Corpus Guideline level 3: "Utterly change the appearance or size of a person" (which is the same base used for Disguise of the New Visage). +2 to up it to Sun duration, and +1 for Part (unless you want to slightly change your whole features including your hair), makes it Level 10. Mu 4 + Co 10 + Int 2 + stress die + any aura = ? รท 2.