Funny that those with Crohn's lack the necessary organisms in their gut that the rest of us have, in that vein

Nope still yourself unless your brain was changed

I think you from today are different than you from a day before. You have a whole day of experiences that distinguishes those two people. The logical conclusion from that line of thinking is that you can ignore what the surgeon does because every moment you are a different person anyway. You never become the other person just like you never become yourself as a child again. The "you" is just a mental construct that a bunch of atoms (or cells) make up to describe themselves at each point in time. It doesn't really exist.