Board Thread:Support Requests - Community Management/@comment-1764483-20130215180421/@comment-3030984-20130215184149

Users are allowed multiple accounts, as long as they are open about having a such accounts (the accounts are not used to bypass bans or for sockpuppetry).


 * For your first usage idea, I would only do this if there was a common misspelling issue. e.g. Eladske is another account owned by me, because it is such a common misspelling of my username. I would avoid doing so to prevent other users taking names similar to yours - that's kinda unfair to people who genuinely use the name you take, and any issues of impersonation can be taken care of quickly by the VSTF.
 * For your second usage idea, do not do this at all. It certainly won't stop a determined user, and will probably start a game of cat-and-mouse of account creations. The best thing to do is block the IP of a persistent vandal.

TL;DR: Don't create accounts fro the sole purpose of preventing spam/vandalism. The tools available to admins (and the VSTF) should be enough to deal with any issue.