Ii would likely need:- (1) A morph target to create the new eye socket. (2) Add the eye (and any eyebrow and eyelash that it may have) as props. Note that if the human `pineal body' grew to the surface and became an eye (as it does in some reptiles), it would surface not in the forehead but on the top/back of the head about 45 degrees behind the top point of the head.