Of course

Goat head, I can eat tin cans and garbage

Goat legs, I can get a job climbing mountains

Yes because if it's the bottom half I get powerful legs and if it's the top half I can always join a metal band

can the transformation be heterogeneous? like I could get a goat arm, goat leg, goat liver instead of just my lower half or upper half getting transformed?

if so, yes. if not, also yes.

Can't I just be transformed entirely into a goat?

imagine you say yes and it's your left half

idk probably not because being vertically half goated sounds inconvenient