Open the "config.ini" file in the game folder with your text editor. Locate the "[Settings]" section and edit the following lines so they look:
ActivateGameCheat=1
ActivateCheatDebugKeys=1
Now you can use the following codes during a game:
Infinite turbo: Ctrl + Alt + O
No damage: Ctrl + Alt + G
Win mission: Ctrl + T
Lose mission: Ctrl + W
Reset all help messages: Ctrl + Alt + M
Reset all collector boxes: Ctrl + Alt + C
Set enemy speed: Ctrl + Alt + E
Damage multiplier: Ctrl + Alt + D