In anticipation for the release of the Assassin's Creed: Brotherhood multiplayer beta release on Oct. 4th, Ubisoft has released two new trailers showing off the characters, moves and new abilities, not to mention locations and multiplayer levels/maps!
Assassin's Creed Brotherhood Reveals: Smuggle Me Tight, Baby (Now, was that video title an Austin powers rip-off or what?)
The second trailer goes in depth and introduces abilities and new game modes, it is on-par in awesomeness with the older trailers released:
The Assassin's Creed Brotherhood Multiplayer beta will be accessible on Oct. 4, 2010 exclusively on the PlayStation®3 computer entertainment system to anyone that pre-ordered the game from GameStop in the United States.
In the Multiplayer beta players will have the opportunity to choose from nine different, default characters such as the Doctor, the Priest, the Executioner, the Courtesan and many more!, try their unique deadly weapons and discover their signature moves.
Up to eight simultaneous players will be able to use new ways to assassinate their targets in two different modes.
As you have read above, my guess is that customization is disabled for the beta, as well as all the modes and newer characters.