I have noticed that the specific entries for “Item Quality Definitions” actually have a quality multiplier listed as one of the parameters, along with durability modifiers. The wording makes it appear as though, when an item of that quality tier is dropped, that variable is used as a starting point for the equation that rolls an item’s random stats - such that any given drop is within a certain range +/- of the modifiers listed under these entries.
If no one else has any experience messing with these variables, then I will begin experimenting with them in roughly another 12-24 hours. When I do so, I will post results - however, I still would very much appreciate knowledge from anyone who knows how to eliminate Item Quality modifiers efficiently from all items in the game. My workstation does not seem to play nicely with the Dev Kit, for some reason, which would greatly extend the amount of effort and time required to find a solution by trial and error. If it were not for the performance/time concerns, I would have been posting my actions/results instead of asking a question first. 
Sorry.
Still, if no one else responds, I will begin the slow process regardless and I’ll start by testing how changing these fields affect the game and reporting the results here.