Editing units for only certain faction

[carions46]

How can i edit units to make it on example like to empire only not other empire provinces?

[Cataph]

Faction-specific variant is easy, just a faction filter in unit_variants.
Do you mean stats? In that case either use an effect (tie it to the LL bundle, or whatever, even Altdorf) or otherwise you'll have to make a clone unit only recruitable by them but I don't recommend going that path.