The cheats are for the original GR, they're not the same for this one. To beat the end of lvl 3 (i am sure you have gone past the tank, its the easy part) take cover behind that cart with the hay. lie down to shoot some of the enemies, and watch out to your right, an enemy will come out by the destroyed tank. after all the enemies are gone, run into the village. do not worry about the other enemies that come ot, but look to the left and shoot the general who is trying to run away.
There is also a path next to the destroyed tank. If you go down it, you can shoot those guys at the entrance from the side. "Trust me, I a game freak"