I know this topic is old and inactive, but I feel like I need to say this.
Most Muslims oppose gender transition because they believe it is wrong to temper with god's creation. But think of it this way, if someone is born with deformity e.g. a clubfoot or a cleft palate, they are allowed to undergo surgeries to fix themselves. So what's wrong with undergoing surgeries when someone is born with the wrong body?
Even the most conservative Islamic sects allow transition surgeries for intersex individuals because they are born with wrong bodies.* Heck! they even endorse it.
Therefore, I don't see any reason to oppose anyone's transition, male or female. We are all just born in the wrong bodies.
So, to answer your question: No, it is not haram to transition.
* I am intersex, and personally, I don't think there's anything wrong with my body, anyway.