I don’t think there’s any Church rules on having a hair transplant. If a man wants one, why not? Just don’t spend money that should be for more important things. As a woman, I’m not partial to a man having a head of hair, skimpy hair, or even bald. Just make sure it looks natural. Ie. If you’re a 78 year old grandpa, don’t go and get yourself a black Afro transplant!
I don’t have any problem with women getting a hair transplant, either. Just have it look natural.