Play as the bad guy
Beat the game as Liu Bei and you get to play as Cao Cao. The game unfolds differently. For example: instead of helping the citizens farm, you force them to farm harder for you.
How to always win Duels and get new duels
This is more of a tip than it is a cheat but to win duels always make sure your moral is higher than the enemies then challenge them and watch them cry and to get different duels I'm not to sure about this I think you pick normal or extreme for your difficulty and you sometimes get new duels.