MySQL username too long, Need to increase the max length for MySQL username

[knight]

I've tried installing vBulletin again on a different website of mine, but encountered a too long of a MySQL username error. I remember I edited something to get it to work a while back, but now I forgot. Is there a file I can edit which will enlarge the database name/user name field so I can stop getting this error? I know its preset at 13 characters (max for MySQL username).