Supposing a Jewish girl wants gender reassignment as male so that she could marry a girl whom she loves dearly. Instead of using scalpel and hormones, every cell in her body is rebuilt as using XY chromosomes, from the molecular level up. We will have this technology in two hundred years, we're on the baby steps of it now, it's called "nanotechnology" aka "molecular engineering". Doctors use the X chromosome from one of her mother's cells, and the Y chromosome from one of her father's, so the new body still has Jewish lineage. She wakes up a fully functioning male, producing sperm, hair, and everything, plus uncut foreskin, so she's a full he now, except for experience which can quickly be learned. Does that new person need a new set of life-cycle ceremonies for him to be acknowledged as a Jewish male, such as circumcision (which seems obvious)?
Given that this is totally fictional, it is really not a valid question. However, on a theoretical level, this would classify as "elective surgery" for a forbidden purpose and should be forbidden. It would (at least) be considered the same as a "body transplant" for the sake of vanity (at least) or for performing prohibited acts. At the very least it would be considered "beged isha" or "beged ish", that is, forbidden wearing of "clothing" reserved for the opposite sex. This is besides the prohibition of self mutilation (which also applies here).
Note that none of the reasons to allow it are indicated in this theoretical case.