the basic system for my mod is that when a tech is researched, another one is randomly set aside. Is there a way to code this ?

I think you can trigger a narrative event with a technology, and narrative event can have random consequences, maybe with that you might get somewhere ?

I gotta tell you that what you're trying to do is not simple, I would advise you to try your hand on a smaller project before going all in on a big rewamp of the whole game.

The whole point of my mod revolves around this idea, of randomly discarding (or at least vastly increasing the cost of) a technology. Another key element is to increase by a little percentage the overall cost of all techs, when a tech is discovered. 

Without these two features, this mod is pointless.

i will gladly have a look into narrative events anyways, thanks for the reply and tip.