Multiple alteration spells?
Yes, multiple alteration spells may be attached to the same unit.
From the top of page 3 in the Plaid Hat Games FAQ about Ashes:

Q: Can a unit have multiple alteration spells attached to it? Can they be the same spell?
A: Yes to both. You may have multiple alteration spells attached to a unit, and you may have multiple copies of a single alteration spell attached to a unit.