I was looking into editing the Heavyweight perk from Dead Money to affect armor as well, however there doesn't seem to be any list or script that tells it what items are covered. A look at the perk itself yields the classification 'Reserved' under the heading 'Data 1', however there doesn't seem to be anything in the GECK indicating in what way it has been reserved. It's an Entry Point-type perk, in case that matters.

To an extent this also applies to Jury-Rigging, as it has neither script nor form list either. I worked around that by editing the various repair lists, which I was doing anyway as part of my personal Repair overhaul.

I really don't want to change the base weight values of the various armors, since that would defeat the point. If I end up having to create a second perk, so be it.

If you're still interested in knowing how the Jury rigging works.
Yes it seems to be hardcoded in the game.

However, for weapons you can use the NVSE commands GetWeapType & GetWeaponSkill. Anything that matches the item you are trying to repair can be used.
For Apparel, it's GetEquipType, and the Heavy/Medium/Light option (for which there is no access in NVSE).
So the best you can do is headgear only, as that is always light.

I've had Dead Money for weeks now but not had chance to play it. I made the mistake already at looking at the code in the esm and running into some spoilers.

I already knew how Jury Rigging worked; what I had hoped to do was be able to edit a perk-specific form list or set thereof, but it doesn't have any. Thus I had to use the 'brute-force' method of editing individual lists in order to add certain weapons to certain lists.

I had hoped to avoid that with Heavyweight, but it's starting to look like I'll have to forgo that particular change as it would appear it works in a similar manner.