Hardline 

Edit the file <hardline.cfg> and add the following as the last line (remember to make a backup before editing the file):

CHEATING IS SOMETIMES USEFUL BUT FOR HOW LONG ???

You should now be able to use the following keys during the game:

        <X>  Immortal
<BackSpace>  Kills all enemies on screen
   <Insert>  Full health
   <PageUp>  Extra ammo for weapon 2
     <Home>  Extra ammo for weapon 1