I already did that! I changed the number in Team ID in the players tab in RED MC but the player still shows up in free agents. But he has the teamlogo behind is portrait though ...
teamID does not decide the team a player is on, only that logo and blacktop uniform. You need to edit the rotation part of the teams tab. For more information on that, click the Learn link in my signature and check out the tutorials on teams and trading players and such.