Okay, for the first few Prestige's, I never used the store. Payed no attention to it. When I hit Prestige Six (I think), I started using it to Unlock extra class slots. I have currently unlocked four slots but I am at Prestige Ten. The Prestige Store is no longer in available for me.
My question is, when I hit Prestige Master, will I be able to unlock another CaC slot? I don't want to have all nine slots and then the one, default Sniper class at the bottom.
I have no idea but if it's not available to you now you may be out of luck. I unlocked my CaC slots with my first 5 prestiges. So I don't have to worry about it but I hope that it turns out alright for you.