How hard would it be to edit P2Pool to run CosmosCoin?
About as hard to edit it for any other coin. I think you just have to state the genesis block and the default ports somewhere.
No, pools for POW+POF is different.
So you base it off the p2pool for PoS coins instead of the original p2pool, obviously.
I'm not goo at making p2pool, but it seems that novacoin, bitgem and bottlecaps don't have p2pool.