Cheats are put to work rather untraditionally: You have to set the variable HELLMASTER to value marking the number of mission, where the new game starts (starting with 1), e.g. (DOS command prompt):
set HELLMASTER=3
signus.exe
In addition to the new game starting with the specified mission, these hotkeys work:
F8 … saves a screenshot
F9 … reveals the map
F11 … ends (succesfully) the mission