8. Roster and Aliases
Teams may only have people in their line-up who are on the squad list of that team. All players on the line-up MUST be registered and their profiles linked to their team. (NOTE: only the roster in this site counts, no other leagues or clan websites.) IF they are not, the clan will get -1 point for each player that is not in the squad list. Player using an alias not listed in roster of the clan the player is playing for is considered not to be on the squad list.

Each player is allowed one account in the Urban Zone website. Each player is allowed one alias per season. An alias must be entered before the player engages in a match. Player names must not be changed during matches. Players are only allowed to change names during the warm-up periods of maps as long as that change involves changing from an alias to a roster name.

8.A Player Names
Different transcriptions of player names are allowed as long as those are easily recognizable, for example Max = m@x = |/|@X. Lower case or uppercase letters may be used freely. Abbreviations of names are discouraged. All names not easily recognizable or abbreviations will be considered as aliasing and penalized accordingly. The acceptability of individual name variations used in game will be voted upon by the refereeing staff if an aliasing issue is raised. The simplest way to avoid problems is not to experiment with player names in league matches.

8.B Clan Tags
All players in a match must wear their clan tag.

- Gnurkus

However that didn't make it to the rules yet (if I don't forget it will be there next rule update). This means that it is not fobidden YET to have more than 1 alias in the list.