User blog comment:Neowitch/Brain Pie and Living Man's Chest/@comment-972068-20120416121303

Well, when Franky was switched to Chopper, he now has the Human-Human Fruit. He probably doesn't transform because he doesn't know how. So if Brook was switched with someone else, they would have the Revive-Revive Fruit.

Obviously from the Fishman Island arc, Brook does indeed still have a soul, which I think is a fancy name for the "mental heart". The brain and the heart are physical objects that the body needs to function. Law can separate people's brains and hearts from their bodies and they're still fine. This probably means the blood and everything is still being transferred through the body, just at different places. For example, if a head eats food, the butt will still poop.

So even if Brook is effected by Law's power, he will still switch bodies, or he can be completely separated and still be able to poop.