Place the following line as the last line in the "hardline.cfg" file.
Type it exactly as shown or it won't work (note case sensitivity and spaces):
CHEATING IS SOMETIMES USEFUL BUT FOR HOW LONG ???
When enabled, the following are the cheat keys:
Code Action
[X] - invincible
[BACKSPACE] - kill all enemies on screen
[INSERT] - full health
[PAGE UP] - adds accessory weapon ammo
[HOME] - adds main weapon ammo