How about a cyborg whose arm unscrews?
It depends. If a person loses an arm and gets a mechanical prosthesis to restore normal functioning, that isn't transhumanist. If they get a prosthesis because they want to be super strong (or whatever), that is transhumanist.
That we have a word implies that transhumanists are looking ahead, and looking for things that not everyone has yet.
Transhumanism isn't about any technology, it specifically refers to augmentation of humans themselves.
This is reminding me of Manny's assortment of arms for different purposes in The Moon Is a Harsh Mistress-- they aren't the center of the story, they're almost a cool background detail.
And then there's the waldos in Heinlein's "Waldo"-- arms of various sizes which mimic the movements of the user. I'm a bit surprised that they don't exist already, but a casual search suggests that they don't.
I just watched this, a very pretty version of "don't try to make yourself different, just accept who you are", and I realized that self-directed change in fiction is a worthwhile topic.
What I'm looking for is stories where main characters change themselves in ways which are basically improvements-- getting beyond the usual human is a plus, but for purposes of this discussion I'm including any significant positive change.
Another big plus would be the character needing to learn which of their goals make sense, and which methods work.
**ETA:** That was a bit of a stub-- HPMOR is partly about Harry and Hermione changing themselves, generally for the better I think (I've only read it once). It would be interesting to see what happens if Quirrell decides he needs to upgrade himself.
*Stranger in a Strange Land* is an interesting partial example-- the Martian language is presumably an upgrade for the human race, but it was developed by and for Martians, and needs some modification.
A *lot* of relatively recent fiction has people learning martial arts. I think appearance makeovers (typically for women) have become less common. I don't think there's a lot of fiction about appearance makeovers for men-- *The Stars My Destination* has one, but it's offstage. It wouldn't surprise me if *The Count of Monte Cristo* (frequently referenced with TSMD) has one.