The Mapuche civ does this in Rise and Fall. It's achieved by using a combo of MODIFIER_PLAYER_CITIES_ATTACH_MODIFIER to broadcast from the Civilization to all owned cities, then an instance of MODIFIER_CITY_TRAINED_UNITS_ADJUST_XP_BONUS to adjust the XP units get. There's also a RequirementSet thrown in there to control which cities get this bonus (in cities with Governors).
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.