Open the "settings.ini" file from your game folder with Notepad. Add the following commands where "1" is activated and "0" is deactivated.

For instance: Add the line "Instagib = 1" (without the quotes) to the settings.ini file to enable God Mode in the game.

More commands than can be added:

oreOverride - Enable/Disable Gore
HUD - Enable/Disable HUD
smartbomb - ?
weakThrax - ?
audio - ?
music - ?
FMVmusic - ?
showFMV - ?
screenText - ?
fullscreen - ?