Is there a way to play as the Papel States?
Nope
You can play with them in the custom battle
Yes there is follow these steps:
X/Program Files/Sega/Medieval 2/data/world/maps/campaing/imperial/decr_strat.Now you'll see campaign playable and campaing non-playable factions.If you wanna play with Papal States wich is under non-playable factions,you'll need to cut it from non-playable factions,and to paste it to playable factions,then save it.Hope this helps you !!!
I Have Tried This But It Wont Work With
Papal States, Mongols,Trimurids And Aztecz But Work For All Other Factions When I Try To Start The Game With One Of These Factions Game Stucks And Then Craches After 5 Mins
I personally tried it and only the Papal States were playable for me,but shortly after I played with them everytime I loaded a game and pressed the End Turn button it crashed.As for the others I can only assume it's because it isn't their time yet.