Ah, yes... It was a left-over from the Kingdoms expansion, and I exploited their usage (as the engine recognizes them)...
Nothing special btw, they are parameters for the AI behavior. Basically, they force the AI to keep (in my case) at least 3 units in settlements whenever possible (base level, and a modifier of 3 units as well starting from the base parameter), so as to decrease the chance of rebellions (because we know, the AI is so stupid which likes a lot to make everything rebel ahah), so they serve as a trade-off
And for the rest, yes you just need to play with the settings a bit and find the configuration you like the most (to increase rebellion, you should boost all the parameters of my base example)...