I was wrong! One actually can change ones sex.
Change sex is probably the wrong way to put it, since it's really just a case of doctors assigning the wrong sex at birth.
See, we have improved our understanding of sex so much in recent years, the way it was defined during my early years is no longer relevant. Sex is a spectrum, not tied to a person's chromosomes or reproductive system.
Therefore, nothing should stop someone from identifying as the sex they feel best fits who they are.
Apologies to anyone I may have hurt with transphobic comments in the past due to ignorance.