Board Thread:Support Requests - Getting Started/@comment-39219938-20190422031834/@comment-1038387-20190422060842

You can change the display in Theme Designer.

Anti-spoofing is an algorithm that checks new usernames for similarity to existing ones, to prevent malicious impersonation attempts. It's unfortunately also in the rename tool, where it often anti-spoofs the renamer itself. You can manually ask for a rename via Special:Contact/general.