I know a friend that got lucky and had his gt changed from lowercase to a fixed word, ex. mine to Mine.
He told me he contacted xbox and had to work his way up to speaking to an enforcement member and the member said, don't call for this ever again once he got hooked up lol.
Worth a try if you ask me. Lmk if you find another method.
It's impossible to do. Their systems don't differentiate based on capitalisation, so they can't swap it or anything for you. They can't alter it on their end either.
As far as I know, they won't do it. I've tried multiple times to do this because they've fucked me and changed the caps on my tags in the past. Even though it was their mistake they wouldn't fix it. If you find someone with a method, please let me know as well. Haha