IDK who still checks this, but I have it working mostly so I'll detail how I did this. For starters I only got it working in third person and I don't know how to change the armor coating, I'll show you everything I found out by showing you how to get to my spartan below (Mark V(b) with Mark VI prototype helmet and shoulders)
1) Open up Halo Infinite and stay in main menu
2) Open runtime viewer and load (you don't have to poke the armor mod)
3) In the search bar top left, search "masterc" (no quotes of course)
4) Click "hlmt(model)" it will expand to show one file, open that
5) In that file, scroll down until you see a folder labeled variants an open
6) To the right of the word "Variants" next to the "count" box, is a drop down menu, switch that to the number 4
7) Scroll down to and open the folder "Regions"
8) In the drop down box for regions, this is where you pick what you are changing (0 for helmet, 1 for legs, etc follow the index sheet)
9) Once picked what you are editing scroll down to and open the folder "permutations"
10) The second text box should be "runtime permutation index", this is where you enter in the index from the sheet for the armor you want in the previously picked region
11) once you picked the armor piece, press "poke all" at the bottom of the screen
12) repeat for everything you want to change
13) when don, load into the multiplayer menu, then exit it and load into the campaign menu. When you see master chief he should be updated
yes sadly, this will not change when you exit the game, so I recommend writing down all your armor index number like I will next to make it quick
IMPORTANT: some of the indexes on the sheet provided by the mod are incorrect and outdated, so you may need to play around. I currently am missing three parts of my spartan myself.
my spartan: