Clone by Conversion: It’s possible, with the right abominations of technology (basically, start with a healing vat and a cerebral bridge, then add evil) – but since you’re just using the original person as organic raw material, the applications are sharply limited. Basically, if you need reinforcements and have the equipment such that this looks like a reasonable way to go, bear in mind that you can get to exactly the same place in the end by popping along to your friendly local butcher and explaining that you’re buying meat for a family pig roast.

In many cases, this also avoids the ensuring war crimes trial, which is often a point in its favor.

(There is also the technique used by… certain intelligence agencies of covertly implanting sleeper agents with a Trojan device that permits an agent or an intel AI to be remotely downloaded into their brain, overwriting their original mind-state. But decent people shouldn’t think about such things.)