you CAN do unique attacks and everything, if you can animate them. but you would still have to replace 1 character already existing in the game, currently there is no way to add a character without replacing an old one, and i dont think that will change in 1.3 either...
when i say add attacks, i dont mean have all the uber moves in 1 character, you will still be limited to 1 generic beam, 1 uber beam, 1 death move etc.