This hasn't happened yet, but what if they had made a Charizard Lv.X.
So, lets say I was playing Unlimited. I have Charizard EX. Could I level up from Charizard EX to Charizard Lv.X?
If so, that would mean I could play4-4-4-4 Charizard.
I don't think you are allowed to do so since in the EX Series, they did not put in Level in the pokemon. Probably they will just print a regular Charizard & a Charizard LV X..
You can play a 4-4-2-4-2 which the Two are LV.X and Normal Versions respectively. But you can't level-Up a Charizard LV.X onto Charizard ex because it clearly does not state that you are allowed to do so.