You can remove poison from a person. But you cannot remove poison from poison itself.
You can transform a Cobalt atom into a Gold atom (by modifying the number of nucleons and electrons and ordering them). But you cannot have the Cobalt atom be a Cobalt atom and still behave like a Gold atom. That is because the interactions are mechanical, and the laws of physics are consistent. In the same way, you cannot change a person without changing the person.
That is, if you change the person in some manner, then what you get is a different person than the person they used to be.