There's only one actual *[rule](http://wiki.warlight.net/index.php/Rules
)* about multi-accounts:
|> You shall not operate more than one WarLight account in a way that gives you an advantage in a game, tournament or ladder.
It has been discussed on another thread whether or not people would be allowed to use three accounts each in a 3-vs-3 where each players controls all colours on one team. Even though (if memory serves!) Fizzer did not officially respond in that thread, most people seemed to agree it was probably okay.
Just be very careful when it comes to tournaments; sometimes people mass-invite everyone they know into a tournament, so you might get invites for both accounts. While both (all) of your accounts joining a single team would probably be okay, as soon as you have accounts active in more than one team (in a 1-vs-1 or FFA tournament that would automatically be the case when joining with a second account), you are breaking the rules.
Furthermore, I agree with everyone else in failing to see why you even *want* to do this, but this is (*my best understanding of*) the rules, in case you want to do it anyway. (Extra tip: you can always ask Fizzer if something's unclear.)