Press X(2), Y(2), click Left Analog-stick(2), Right Analog-stick(2), press L(2), R(2) at the main menu. There is no confirmation message. Start a game then pause and enter the options screen. The "Cheats" option will be unlocked at the options menu, with "Trooper Level", "Enemy AI", and "Mission List" selections. Note: Do not set the "Trooper Level" option to "Full", as one bullet hit will take half of your life away.
Last resort attack on tanks
If you need to take out a tank but have no more long range rockets, it is possible to get close to it without getting hit. First, you will need to have a sniper rifle to zoom in on the top of the tank to take out the gunner, if there is one. After he is down, throw a smoke bomb in the direction of the tank. Try to get the smoke bomb in as close to it as possible. While the smoke is in the air, you can run up to the tank without being hit. The smoke will make it impossible for the tank to see you. Get directly next to the tank and plant a C4 next to it. After it is planted, throw another smoke bomb slightly further away from the tank. Make a mad dash for the smoke. If you are fast enough, you will get behind the wall of smoke and can then make your way to safety. Then, detonate the C4.
Spreading out munitions
Do not give too much of the powerful items such as tank mines, C4, anti-tank guns, etc. to a single person. If you have this person advance and he gets taken down by a tank, your other teammates might not have the firepower needed to even get close to the downed person, let alone heal him. It is always a good idea to have each teammate equipped with at the least one high powered explosive in case you need to take something out.
Weak spots on tanks
All tanks have very heavy front and side armor. However, the tank's rear is lightly armored. Smaller tanks can be hit with a rocket almost anywhere and will usually explode. However, larger tanks must be attacked with an explosive from behind. If you shoot it from the front or side, chances are you will not even make a dent.