Season Mode Rookie Challenge rosters

Is there any way I can choose the rosters for the rookie and sophomore teams in season mode? I tried to edit the players.dbf in my saves folder, but doesn't seem to work...

You should be able to, but you'll need to wait until the All-Star Weekend comes around so that the teams are generated. From there, it should just be a matter of editing them.

The thing is I can't even create players in season mode, and when I tried to look for the players on the sophomore or rookie team in the players.dbf file, I can't seem to find many of them (with team# 44,45). It seems like these two teams are generated by the simengine, and they are not stored in the players.dbf when I tried to save. Any thoughts?

They definitely aren't generated until the All-Star Weekend comes around, if that's what you mean.