Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. Use a text editor to edit the "bia.ini" file in the "system" folder in the game directory. Look for the "[Engine.GameInfo]" heading, then enter the line "bCheatsEnabled=True" below it. Then, look for the "[Engine.Console]" heading and change the "ConsoleKey=0" line to "ConsoleKey=192". Then while playing a game, press ~ to display the console window. Enter one of the following codes to activate the corresponding cheat function. Also, there is no confirmation that a code has been entered correctly.
Result
Cheat Code
God mode god
Flight mode fly
Disable flight and no clipping mode walk
No clipping mode ghost
All weapons allweapons
Extra ammunition allammo
Togle invisibility invisible [0 or 1]
Kill everyone killall
All items loaded
Remove all items unloaded
Old Movie mode oldmovie
Toggle blind AI blindai [0 or 1]
Toggle deaf AI deafai [0 or 1]
Toggle blind enemies blindenemies [0 or1]
Toggle deaf enemies deafenemies [0 or 1]
Map select loadspmap [map name]
Spawn indicated item summon [item name]
Unknown supersquad
Unknown lightperiod
Unknown lightcone
Unknown getfirstmission
Unknown pawnanimextra
Unknown soundocclusion
Unknown smiteevil
Unknown avatar