Based on what happens with IDCLIP and IDBEHOLD, I tried a few other cheats, and you can get some very interesting messages with these. I tried: IDDQD (different messages for on and off), IDFA, and IDCHOPPERS. If you try IDKFA or IDMUS, it basically just tells you it won't let you do those things. The same might be true of IDFA too, but I'm not sure; given the nature of this map, it's possible that it actually is a clue.