Well, that username you want is already taken, for one
I want to change my username to...

Actually doesn't matter, it is still unusable. Keeps someone from starting a new account posing to be the other guy.

Actually, you do not. A friend of mine has never sent a cent to chesscom, but he has changed his on multiple occasions.
I was thought that I can change the name of @padaq to @Cheetah, but I don't know what you think my name is fine or I request that they call me @Cheetah.