Launch the game with these command-line parameters
to activate cheat modes:

-mumford - Hodspodkins Mode
-whostayedlate - Rockhard Mode
-whostayedlateagain - EasterEgg Mode

Example:
"C:\Expend\go.exe" -whostayedlate

---------------
Various Cheats
--------------

Type in the following codes then press "-"
on the numeric keypad to activate

bod - Enable cheat mode
bing - Disable cheat mode
dunky - Highscore entry and back to main menu
bucketofchicken - View from behind
babapapa - More credits
bungle - ???
crystaltips - 1 additional life
albertofrog - Super granades
mrbenn - Skip level
zippy - Infinite health
triz - Triangle info