I just saw this and, since I'm not accusing anyone, I'm curious if deliberately changing username to match the username of a diamond moderator is within the rules of Stack Exchange.
Identity Theft and Privacy. Users that misleadingly appropriate the identity of another person are not permitted. Users may not post other people's personally identifying or confidential information, including but not limited to credit card numbers, Social Security Numbers, and driver's and other license numbers. You may not post information such as other people's passwords, usernames, phone numbers, addresses and e-mail addresses unless already publicly accessible on the Web.
Also, keep in mind that the discussed case is using username that is rather distinct (there are other "Tim's" on the site and I wouldn't bother if anyone used same username as me, I probably wasn't the first one as well). Moreover, it was about using username of one of the diamond moderators of this site, so this may lead to impersonating the moderator.