To have your digimon tamer in a different outfit, hold L1+L2+R1+R2 while selecting your digimon.
Note: Works only with Agumon,Gabumon,Patamon,Wormmon, and Gatomon
In case you didn't realise, the English passcodes doesn't work for the Japanese version of DRA. The codes serve as the same purpose as the North American version, to unlock characters.
To let both players select the same character hold ''Select'' while choosing your character.