Changing Sex In Islam

It is not allowed in Islam to change the gender, and doing so will be changing of Allah’s creation.

And surely I will lead them astray, and surely I will arouse desires in them, and surely I will command them and they will cut the cattle’ ears, and surely I will command them and they will change Allah’s creation. Whoso chooseth Satan for a patron instead of Allah is verily a loser and his loss is manifest.He promiseth them and stirreth up desires in them, and Satan promiseth them only to beguile.
4 Surah An-Nisa (119-120)

the hermaphrodite gender is an exception. only a sign of Allah’s Power of creation, for a wisdom He knows better.

The only exception is related to a person who has both genders potential in body, so a medical treatment can be sought to unify one gender. In this case it will be a correction, and not a change in the creation of Allah, the Almighty