Which you could do before by editing things or using a mod...for free. The CK+ mod that I already had let's me play Muslims and Pagans and already expanded into that part of Africa that they added.
Except you don't get the decadence modifier that adds more realism and you can't patch the game until the mod gets patched, the game is called crusader kings playing Muslim wasn't how you play the game, I personally will buy the dlc, because like all PDox DLC its worth it