This will only work with Steam Versions 1.3.643.1 and 1.4.651.0 !!!
This will overwrite the "Patch2.000" file. Verifying the game Cache Integrity will revert back to vanilla.
The "Ignore Player" function isn't what I'd expect it to be; make noise or bump into someone and you will be heard or spotted.
The "Infinite Ammo" option has a tendency to reset itself back to "False" after a reload of a savegame and sometimes after a cutscene.
All options will be reset to "false", when you exit the game. So when you fire up your game, you'll need to set all your desired options back to "true".
Remember, I did NOT make this!
I'm merely providing the Missing Link (okay, bad pun!)
P.S.: I don't know whether installation of the DLC will affect the usability of the Debug Menu.