“I Know You’re In There Somewhere” Fight: Averted. If you think one of these is going on, you’re being Wrong Genre Savvy, and quite possibly, you’re being suckered by someone who thinks that they know that you’re Wrong Genre Savvy. Neither downloading-and-replacement, nor editing into compliance leave the original person in their brain, never mind capable of doing anything. Nor do possession or puppeteering leave them any way to control their own body, under virtually any circumstances.
Standard procedure, therefore, is to kill the zombie and restore from backup. If you need the information they might have acquired before getting caught and pithed, well, shoot to incapacitate and hope that once you get their brain back to the lab it turns out to be a quick-and-dirty puppet job, because that’s the only way it’ll be there any more.