slowing research

[Alneyan]

You could probably give a negative research ability to every single unit in the game, if you knew the range of unit ids; doing it by hand would be Tedious, but it should be straightforward to generate automatically. Well, assuming all possible unit ids are known in advance.

I don't think you could use percentages that way, though. Still, setting all mages to have only one research point, period, and then playing with the Magic research setting might do the trick for you.