Do you mean changing the user name, or the Keymaster title? There’s no easy way to change the user name. Just make a new user with the name you want, then promote them to keymaster, then log out, log in as the new user name, and delete the old keymaster if you want.
Changing the title of keymaster is easily done if you log in and edit your profile. There is a field called ‘custom title’ where you can set this to anything.
I chose a Keymaster title during installation the very first time that I wanted to change. Is that possible?