Well I looked it up and found it at the following site:
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The paragraph on it reads:
"
Easy Veteran Mode:
At the mission selection screen, choose a mission on the Veteran difficulty. After the first checkpoint, save the game, and quit. Go back to the mission selection screen, and choose the same mission, but change the difficulty to Recruit. While the mission is loading, you will see a white bar at the bottom of the screen. When the bar reaches approximately 33%, eject the disc or go to the Xbox Live Dashboard. Then, reload the game, and select "Resume". You should now be playing the mission on the Veteran difficulty, but with Recruit AI.[/i]"
So keep in mind you can't play it like recruit sprinting and destroying everyone. Since the damage modifier is still set to Veteran they still take you out in a couple shots. But I find this cuts down on the ridiculous amount of grenades the enemy throws at you. So using this I was able to make it all the way to "Burn 'em Out," which was a big improvement from my first attempt at Veteran never making it past "Little Resistance." I would have kept going but I have come into a copy of the God of War Collection and have jumped on that at the moment. Sorry it's not an all out guide like you may have hoped for. I'd also like to add. I do this for everyone mission rather than once and continue playing. I'm not sure if the glitch holds cross missions like that and I haven't wanted to take the risk to try it, so just to be safe I'd continue doing it for each mission if you're interested.