Change Statistics
Editing the "actor.ltx" file in gamedata\configs\creatures can allow you to change player statistics, adjusting how much damage you take and the amount of weight you can carry. Look for [actor_immunities_gd_****] and replace the stars with 2.0 for double damage, 1.0 for full damage, 0.5 for half damage and 0.0 for no damage. Editing the number associated with "max_walk_weight" will change the maximum kilograms you can carry.
Freedom Armory
This cheat will allow you to enter the Freedom Armory without being detected. When approaching the guard, push a chair into him and then jump on to the chair and then into the guard. A glitch in the game causes you to sail past the guard and into the armory hallway. Use your knife to slash the door's lock and enter the armory. The same chair technique will also help you exit the armory.
Upgrades
You can upgrade your weapons at the Duty Base, so make sure to collect as much money as you can early in the game and purchase more powerful weapons. You can also upgrade items at the Freedom Base, buying a new suit and better equipment. Unfortunately, bandits will rob you when you leave the base, stealing all your equipment and money. You can track them down and retrieve the equipment, but the money is gone forever. So make sure you spend all your money on equipment before getting robbed.
Secret Artifact
Exploring a cave deep in the Dar Forest will reward you with a secret artifact. But be careful, because bandits and poltergeists call the cave home. If you manage to avoid your enemies, you'll discover the artifact resting on a table. The artifact provides you with a +6 endurance and doesn't come with any negative consequences. Later in the game, you have to give the artifact to a man named Forester, who trades you an upgraded Vintar BC rifle for it.