By default, you have 5 Custom classes unlocked right? So, on the trainer if you select 5 (the first option) it won't unlock anything, if it does, then I screwed up . The last Option, 10, unlocks 15 classes (10 + 5 (default) = 15 )
That means... if you want to go back to 5, select the firs option. Don't need to be afraid to play with the options.. I'm quite sure no one will get a ban for this.