During gameplay, hold down TAB and hit the page-up key
 simultaneously. Then let go and press the letter P. At the bottom
 of the screen it will say "cheat enabled." This will make you
 indestructible. This won't help on missions where you have to keep
 other things, like the War Drum, from blowing up, but it will help in
 those nightmarish combat situations. 
 
 Or you may try this alternate cheat:
 
 HexEdit dl.cfg
 goto offset 00000358
 change that byte to 32 hexdecimal
 save & exit.
 You can now choose any mission you want.