slowing research

[BigDaddy]

Those setting being a "house rule," would be problematic for some nations like Ulm (in a good way), Atlantis (in a bad way), and Ermor (in a bad way).

[Saber Cherry]

First, try playing with Very Hard reasearch, in the game setup... in case you had not yet noticed that setting. If research is still too fast, here are a few more suggestions in addition to the ones above:

Mod Owl Quills, Lightless Lanterns, and Skull Mentors to cost double or more. I forge an Owl Quill for every researcher in every game that I have access to Air magic, for example.

Increase the price of sages to 120g or more.

Those 4 changes will result in a very tiny mod that will be easy to make, and might slow down MP research by 50% together. In a single-player game, I doubt they would have any effect, since I doubt the AI makes good use of sages and research items.