Sociologists define gender as a socially constructed category and that people can transition between these categories. See here.
https://www.thoughtco.com/sociology-of-gender-3026282
>Gender, on the other hand, is a social classification based on one's identity, presentation of self, behavior, and interaction with others. Sociologists view gender as learned behavior and a culturally produced identity, and as such, it is a social category.
This opens the floodgates to other socially constructed categories (e.g. race) among which humans can transition. However race is too politically controversial, so instead I'll tackle this from another angle that's less controversial, and less ambiguous as well.

Royalty is a socially constructed category, right? The notion that someone is a monarch and that others are peasants is a socially constructed dichotomy. People can marry into royalty, or even renounce royal status. Each category requires different social customs. As such, if I'm born as a peasant, yet I identify as a king, and if I feel I was born into the wrong social category, could I socially transition into a king? I begin dressing more regally, I get a tattoo of a crown on my head (pic rel), I begin behaving more regally... am I now a king? If I tell you my preferred pronouns are "your grace/your majesty/my liege", are you obligated to address me as such? If I tell you to bow in my presence, as peasants must do around royalty, would you oblige? How about if I called you regalphobic if you refused?