This is the tutorial for basic halo modding
Ok, first off, you need a hex editor, and some offset lists. Check the essential files and stuff section for links. Now that you have the stuff you need, lets get started. (its easiest to understand if you are reading this as your doing it)
First of all, read the explanation section also. This will help you out with everything. Now, we are going to start off by making the Warthog gun shoot rockets, and change the ghost into a banshee. We are going to do this on Blood Gulch. Ok, so to make a gun shoot something else, you would edit the projectile part. Now, we want to find the Warthog bullet. So, open up your offset list, click on projectiles, then look under bullets for the warthog bullet. Ahh, there it is. Now, you will see four colums, each with a number in it. (Check the explanation section for more) The one we want is the offset. This is where the value is stored. Copy the offset, go into your hex editor, load up blood gulch, click down the edit bar, click goto, and paste the offset into the box.(The offset it 00856BF0 ) Then press enter. It should take you to the value of the warthog projectile. There will be a bunch of numbers. Now, minimize the hex editor, and go back to your offset list. Now, you wanna change the warthog bullet to the rocket right? So, find the rocket in the projectile section. Now, this time, you are changing something into the rocket, not the rocket into something, so you want the value (second colum). Now, you cant copy/paste this, so I suggest you write it down. (The Value is 6C3B7340 ) Now, bring back up your hex editor. Now, just type in the exact value (it will just over write the old information). Now, save your file. If you did everything right, your warthog should shoot rockets. Now, lets replace the ghost with the banshee...
Now, you are going to do much of what you did last time. Open up your offset list, click on vehicles, and find ghost. Now, copy the offset, past it in the goto box, then minimize your hex editor, find the value of the banshee, and overwrite the old value. Now, save your file, and if you did it right, where the ghosts were, there are now banshees.
Now, the main reason I did the second part, was to show you that you can offset swap alot of things. Dont like the sniper, change its value to another gun. For some cool stuff you can do with offset swaping, check out the advanced offset swapping section.