Put the pointer on the spare book on the left and hold Select then press: R1, L1, L2, R2. Your troop roster will now contain every available unit in the game.
In the mission where you're rescuing Ilmarin or later known as Ceridan, go to the snowman at the top of your map and place one of your regiments next to it(i recommend the cavalry). Anyway, there will be a magical sword inside the snowman: The Dragonblade!
All the cheats have to be entered on the caravan screen.
Put the pointer on the troop roster and hold Start then press: Circle, Triangle, X, Square, Left, Right. Now your troops will fight for free.
Put the pointer on the book of magic and hold Select then press: Left, Up, Right, L1, R1. Now whenever you cast a spell during a battle, no magic points will be deducted.