If a character returns as a drone, will they still retain their regains?

Also, quick questions about the surgeries--can the results of the surgery be reverted via surgical means? Like if a character knows another character who is good at non-magical surgery, can they replace a malfunctioning prosthetic given to them by Mrs. Johnson with a better functioning one? What if they tried to transplant another character's healthy organs into the place of their now messed up ones?