This trick will exploit a fatal error when applying the +set developer 1 +set sv_cheats 1 command line parameter, if you get the "You cannot cheat on the server" message. After starting the game with that command line parameter select a new game (or "Resume" a current game and the cheat should work). Set the level and start it. Then, save the game and exit out back to Windows. Restart the game and select "Resume". Do not manually select a game to load. All you need to do is "Resume" your current game.