Concubinage/polygynia is, to the best of my knowledge, hardcoded - many total conversion mods have had problems precisely because of that. Default and opinion penalties are partially already changed (except, it seems, for tribals and stuff - if so, it is also hardcoded; though I could also change something in defines.lua). That is an interesting idea overall, but difficult.

could you create another mod that replaces all the male-preference succession laws with female-preference ones, so that ai by default has enatic or enatic-cognatic, and has opinion penalties against male heirs and rulers. also swich all the restrictions so that, for example, female pagans can take concubines, and muslim females can take 4 wives, while the men cannot. basically, do a feminist's dream reality by changing everything that refers to men, to refer to women, and vice versa, apart from obvious stuff like pregnancy

By "the laws" I meant Conclave gender laws, of course.

By the quoted I literally meant that you don't have to be Cathar or Basque or whatever to get true cognatic or change the laws to get agnatic-cognatic.
Firewing - change "always = yes" to "ai = no" in "potential" scope for all successions you want to limit to yourself AND do what described lower to change the default if enatic-cognatic is among them.
As for enatic-cognatic - works as intended but easy to change. Just move the "default = yes" and the default_selection part to the succession you prefer to be default in the succession_laws.txt. And I suspect vanilla AI is sexist so they wouldn't change to it without some serious tweaking of AI behaviour - way beyond my current skills.

at the earlier start (769), most of Empire/Kingdom/Duchies titles are with enatic-cognatic law, especially in Europe. It's maybe better if you let those titles with agnatic-cognatic law. It can be interesting to see the AI changing succession law to enatic-cognatic by himself

Sorry to bother you but would there be any way of making this mod without it applying to the AI as well? It'd be nice if I was the only nation who preferred female rulers and everyone else hated me for it.

what do you mean by "destroys limits on agnatic-cognatic (male-preference) and true cognatic successions" ?