How to replace ai with human midgame? (multiplayer)
If you select the Internet option when playing a game - you can in fact have a player take over an AI - and have an AI take over a human player.
To do this, you'll need a saved game when playing a previous multiplayer game (you can play single player on muliplayer mode). Then, host another game, load the saved game, and mark the AI you want a human to replace as open, and any human players you want switched to AI as AI. Start the game up, and voila!