Through the use of HMT, Halo PC can be changed quickly and easily. While some mods can take time and energy to do, removing the turret from a warthog can be quite simple.
MAKE SURE TO BACK UP ALL MAPS BEFORE MODDING THEM!!!
Step 1: Open Halo Map Tools
Step 2: Change Textures
Find the tab for bitmaps, and click the plus button next to it. Then, find the texture entitled Levels/a10/cryo glass, and copy the numbers CA161C from the box next to the word "Meta".
Then, scroll down and find the texture entitled vehicles'warthog/bitmaps/ warthog chaingun and paste the code into the box next to the "Swap" button. Press Save.
Step 3: The End!
Launch Halo and admire the look of a warthog without a turret.
Step 4: Optional-Disable Turret
To keep the now invisible turret from shooting, go to the Weapon tag and find the warthog gun. Then, scroll down in the properties area and find the projectile drop down bar. Select 1. Set the projectiles fired to 0, and the turret will now be disabled.