As I understand it, this thread is a case of demonstrating absurdity by being absurd. Yes, Caitlyn Jenner would indeed be required to become Bruce Jenner again to qualify for baptism as one of Jehovah's Witnesses. In addition, she (now he) must renounce all claims to being a woman and complete the re-transition into a man. Any genital mutilation or hormonal issues that would come as a side effect would have to be taken care of by Jehovah after Armageddon once He makes Bruce (formerly Caitlyn) into a perfect human being.
It's a shame something like that didn't happen while the person still was officially in the organization, because that would make for one hell of a local needs talk.