There doesn't appear to be anything in the wiki, and it's not clear just from poking around in the editor. The category is determined by the keyword on the armor or weapon but there isn't any way to edit what it maps to, nor is there any way to add new keywords from the look of it.

This is functionality that the GECK for FO:NV did have. Was it taken out for some reason? It's going to get really tedious with weapon and armor mods if anything new has to be crammed into the exisitng categories.

Wrong board. You want the CK board.

Ah, good point, cheers. If a mod sees this go ahead and close it please.

Ones lurking around, so you may get lucky.