Note: This information is for the Nintendo 64 version of Ogre Battle 64. To do this in VC version of the game, all you need to do is save your Ogre Battle data to an SD card.
Ogre Battle 64 can save 2 files at a time. It also has a quick save file for when you need to quit during a mission. The game also takes advantage of save packs. This page will explain how to use the save packs.
Save Pack Management
All you need is: Copy of OGRE BATTLE 64, and a SAVE PACK with 25 notes open or more.
Insert your copy of Ogre Battle 64, and place a save pack in the back of your controller. Hold 'START' and turn on your Nintendo 64. You will then enter into the management screen of your save pack. Here you can move save files on and off your cart.
With this, you can save as many game files as you want and beat the game multiple ways without losing old save data. Each Ogre Battle 64 file will take up 25 notes.
Ogre Battle 64 and all related material is (c) Quest/Nintendo/Atlus/Square Enix