I'd think that
-The mind rejects the body completely, becoming a spirit, or wouldn't properly join to the body; becoming like a puppet
-The mind rejects only the alterations, so it would just look like an abomination
-The mind thinks the body looks swell, so accepts (eue)

Oh! And one other thing! Assuming the phylactery fills the mind/spirit with power to go into the adult body, what were to happen if it was only able to control the power for a small amount of time (as i'd imagien ti would);only enough to quickly fuse into the body? What if it didn't fuse quickly due to alterations or some such? If so, would it be possible
-The mind would die due to the power consuming it
-The mind would release the energy into the area around it, and remain as a spirit due to its hatchling and/or adult body being destoryed/not having enough power to return to its hatchling body after
-The mind would become blighted; therefore becoming a blighted ghost (off the fact that you fill the phylactery with the energy of blighted things)