Create a MTW shortcut on the desktop, select properties and find this line "C:\Program\Total War\Medieval - Total War\Medieval_TW.exe" add -ian on the end so it looks like this:
"C:\Program\Total War\Medieval - Total War\Medieval_TW.exe" -ian

Then when you play you press g to enter godmode were you can do alot of stuff.

Shifting factions and facing your own Behemoth to a facction is quite fun , although the risk of losing is considerble.