To enable cheat mode, you'll have to change an existing game file. Before doing so, make a copy of environment.cfg. Then text edit the original document, adding the line: CON_ENABLE=1.

Once this is done, start the game. Press ~ to bring up the console, then enter one of the codes below to trigger its function:

Cheat menu: cg_menu cheatmenu (Once you activate, use the ~ key to see a menu that allows for god mode and more)
Have all items: cmd giveall
No clipping: cmd noclip