I have an idea for a mod, and rather than blatantly copy some of your code I thought I'd run it by you and see if you would like to help.
To summarize what I want to do
Create very expensive researches that increase the next_probability of the quality levels, one set of 9 for each quality tier so after all 27 of them are done, you are guaranteed a legendary item IF quality is triggered (which is still based on the modules used)

I could tackle this myself, rather clumsily, as LUA is not my strength. Help would be very much appreciated!

On a conceptual level, that is not for this mod. All current researches solely affect the player characters, and not the factory. Even movement speed is a borderline addition, since it makes combat a lot easier, but it's a worthwhile tradeoff, and still technically falls into the category.

On a technical level, these sorts of prototype definitions cannot be changed on-the-fly, so it'd require a script to run every time something is crafted. Suffice it to say that this would incur a massive performance penalty.

Turns out you can't edit the next_probability of the qualities :(