I once tried to make each clothing item a mod. The idea was to have a mod for mining etc. so that the player doesn't have to keep changing clothes.
I was not successful, if I remember correctly, there was a problem with the display showing the levels. It wasn't clear that the game understood what was happening. I didn't pursue it for a number of reasons but you can try copy armorAthleticOutfit into item_modifiers.xml and convert from an item to an item_modifier and see if it works for what you want it to do.