Additional ammunition -
Note: This procedure involves editing a game file; create a backup copy of the
file before proceeding. Use a text editor to edit one of the "level_*" files in
the game folder. Locate the "//Bullets, Projectiles, Missiles" section and
increase the three numbers that follow the "Ammo" entry that is underneath to
set the amount of bullets, projectiles, and missiles (in that order) that will
be available in that level.

Change enemy aggression -
Note: This procedure involves editing a game file; create a backup copy of the
file before proceeding. Use a text editor to edit one of the "level_*" files in
the game folder. Locate the "//Tank, Jet, HelicopterGun, HelicopterRocket"
section and decrease the four numbers following the "Aggression" entry to lower
how difficult the enemy tanks, jets, helicopter guns, and helicopter rockets (in
that order) will be in that level. Note: The numbers must be from 1 through 9.