Gender Bender: Fairly trivial to achieve with Empire-level biotech, whether done by growing an opposite-sex bioshell (or, y’know, other sex; it’s not like hermaphrodite and neuter haven’t been invented, and not every species uses the same sexes anyway) and mindcasting into it, or if one is of one of the clades that has the facility built in (hermaphromorphs).
Also, not exactly uncommon. It’s distributed much like the Kinsey scale mentioned in Bi The Way; while there are at one end of the notional scale people who have one preferred sex they use all the time, and at the other end of the scale people who change sex about as often as they change pants, the majority of people are somewhere in the middle and are mostly/but sometimes. Certainly, it would be very unwise to assume that the person one’s talking to had always been the same sex, even if only just to see what it’s like.
(ObControversy: Gender-identity-wise, the processes use involve rewriting the subconscious – but not the conscious – aspects such that one feels comfortable in one’s new body. After all, it would rather suck having to figure out how these new organs work and what they’re telling you, or having to relearn how to walk ’cause your hips don’t work that way any more, etc.
*Here*, some people would undoubtedly suggest using that to “cure” transsexuals, rather than the equally possible “so, change your sex to what you feel it ought to be, already” option.
*There* – well, a people who worship with fluency, fervor and zeal at the altar of self-identity and personal autonomy aren’t, obviously, going to have any truck with that idea. And, if asked for an opinion, would tell people to go with whichever option they felt best represented their own concept of themselves, because who you want to be is your own damn business, other people’s narrow views and naturalistic fallacies be damned. [In practice, I suspect that usually means the latter option.]
And on an authorial note, I find it preferable to depict a society that refrains from being assholes even when the technological option exists rather than ensure that the option doesn’t exist because many-real-Earth-humans would be assholes with it. YMMV, but mine feels no need to project monkey-brain phenomena on the rest of the universe. It has its own.
Here endeth the speechifying.)