If I could, I don't think I'd really like to change much about my body because I'm happy with who I am. I'd like to live forever though, that's the only superpower I would ever want. I would gladly live forever. If time begins to speed up and I see people withering dying around me like flowers I'll just opt out, but hopefully not before I see this ride to the end. You know, heat death of the universe and all that. I'd really love to see mankind in a trillion years time, long scale. Fly to other galaxies, maybe go back in time if it is possible.
I'd probably make a point of looking pretty much the same as I am now (i.e. an unchanged human) so I remain an example of what humankind was like all those years ago. I'll be able to freak out all the bald, bug eyed, small-nosed greys that make up our descendents by waving my beard at them and wriggling my toes. By then I would look like Old Father Time. I'd wait until all of the information that I know now about our history and the earth dies and fades away so I can tell the greys about the glory of Scotland, how it was always free and independent and the greatest power on the planet. How we subjugated our enemies and eventually became so powerful that we transcended the mortal plane. Maybe one day I will convince them to worship Scotland as a heavenly Rome-like entity. They will not understand, perhaps disbelieve me, but I will let forth a peal of earthy laughter through my mountainous beard, speaking in ancient, millenial tongues unknown to them. Calling them gusty arse weasels perhaps.
Whenever mankind would render itself nearly extinct somehow, I would seal myself in a grand temple (to pay for it I would invest 10 pence in a bank and leave it for a million years or something) and begin growing my beard for centuries with teams of robots (dressed as monks) who would write the history of the universe in the braids of my beard, using a variety of codes and messages. My beard would fill the halls of the temple providing future explorers with information about everything from the big bang to oil paintings to Sudanese football scores. All references however to religion, genocide, murder, greed, capitalism, the general cruelty of man and Fife would be removed. Even masterful paintings would be recreated, such as the Mona Lisa. The hairs of the beard would be woven tightly into sheets, then painted. When the survivors of the apocalypse find me amongst the folds, I would then found my religion.
As for transhumanism in general I take the approach that technology and transhumanism is natural. Humanity is a part of nature, and if we manipulate ourselves, we aren't "going against nature", we're just a part of nature making a decision.