If a society has advanced medical technology where changing your body is not just possible but broadly available, then it follows that they have solved any issues with rejection and adaptation. Nanobots constantly tweaking hormones? Your mind and memories simply layered over a virgin clone brain with everything set for whichever sex that body has?
If the writer set out to explore that theme they might delve into it, otherwise all that matters is that it works and sounds plausible from within the context of the story.
Scifi is about 'what if?' and how that affects people. 'What if money could buy a body of the opposite gender?' is all that is relevant.
Similarly, we don't need to know how the huge space station capable of destroying a whole planet in a single shot works (unless you are a rebel princess), just that it does.