Unlimited prestige points
Simply clear a city of enemy units and put one of your units within the city. Now cancel the moving your units into the city to keep the prestige points you earned. Redo this metho to gain an unlimited amount of prestige points. Note: This will only happen if the difficulty is above 100%.

Play both sides
Just select to play by email when your at main menu. Save your game, then load it again. You are now able to play as both sides.