In addition to the different historical scenarios, you can also unlock options to change the feel of the game. Time limit on gives you until 1600 and off gives you until winter of 2000. Annex options change how you can take territory from the enemy. Once unlocked, changing fief owners can be done by pressing select over the fief.

Code - Effect

Adjust Annex Options - Unlock (recruit) 100 officers
Adjust Officer Limit - Unlock 50 Policy Cards
Adjust Time Limit - Clear Empire Mode
Change fief owner and default officers - Clear Empire Mode
Officer Death Options - Unlock 50 weapons