I have always felt that their is a big difference in player and character reality.
Character reality has it that once you are at a level you can never change.
Player reality is that the game must be fun. If a player really really wants to play a Psi Cop than I (as GM) shouldn't really stay in their way. Now I might choose to try and talk them out of it, if it doesn't really fit the campaign, but I will never outright demand that they give up the idea. This is pretty much the same thing, the rules say that they cannot EVER get the Psi Cop prestige class due to their psi level. I say that is unacceptable. Following that I would find some way to increase their p-rating so that they can gain upper levels.
I could do this in character - they just realized that they had unseen block in their minds, they are actually P12s, congratulations. Or maybe, though training they have unlocked their true potential which was P12 not P10 as they orgionally thought. etc. I would never allow game rules to restrict player fun.
This is the same thing I do with any prestige class. If a player (say a human) wants to take a class whose description is based on Narn. If they can find a way for the class to fit humanity - even if they remove the organizational listing or whatever - I might consider removing the requirement Race: Narn so that they can get it. Its the same with feats and whatnot. I want my players to have fun and to enjoy their characters, not be forced into areas or forced not into areas.
Just my idea and information on how I run games, do not take this as a personal attack on anybody's point of view.
