Load the game with the "bshift.exe -dev -console" command line, then press ~ to display the console and type "sv_cheats 1" to enable cheat mode. Next, enter the following codes at the console:
God mode: god
No clipping mode: noclip
No target mode: notarget
Set gravity (800 is default): sv_gravity [number]
Set jump distance (10 is default): sv_accelerate [number]
Set skill level (1 is easiest): skill [1-3]
Level select: map [level name]