Anyone can change if they will themselves to do so.
And I understand that, but in cases like this game's story, or other fantasy/sci-fi games (of which I feel this game could be considered a bit of both) there's most of the time going to be some beings which have no gender, in fact, snails are hermaphrodites, and technically, therefore have a single gender. I realize that we are not arguing, but I like talking and saying stuff I know.