Type SS ADN in the menu, now you have:

 Dark20000   20.000 money
 Darkpower   Max energy
 Darkinv     Invulnerability


When playing the Freedom Guard the skirmish tanks always seem so
fragile compared to the enemies plasma tanks. Well now you can
give your skirmish tanks the same characteristics as the plasma
tanks.

There is a file called 'units.txt' in ..\darkreign\dark\deftxt
dir.

You can edit this file, search for the Freedom Guard tank
settings. Look for the 'Setstrength' entry and set your units
strength to around 500. There is another field which sets the
price and buildtime set this to say '50 1'. This will give you
cheap tough tanks for around 50 credits and they will be built
really quickly.

Note: You can do the same for the spyder bikes and tank hunters.

Also there is a file called 'build.txt' which you can set the
cost and increase the toughness of your buildings in the same
way.

This works for all missions up to the 6th one. This is because
there is a dedicated dir and units.txt file for this scenario
which you have to also edit in the same way.

Trounce those Imperial swine with weapons to match their own...
Ho Ho!!

More cheats:

Select any mission:
Edit the file DARK\SHELL\SHELLCFG.H and change the line "#define
BTN_MISSION_COEFFICIENT 150" to "#define BTN_MISSION_COEFFICIENT
157". You can now select any mission from the dial by pressing
the new CHEAT button in the bottom left corner.

How to play the bonus level:

There's another level after the 12th one : Death Blow. To
activate it, go to the level selection screen and click on the
spiral after you've completed Level 12.