Atm I first plan to put custom era's in the mod (Settlement -> Colonization -> Exploration if everybody agrees with those names) and relink the techs/cityart to them. And link the city-audio to the Final Frontier mp3's. It's a bit sidework, I know, but since a number of those features are still on representation graphics I don't see a hurry for doing it. You can try to tackle it if you want, and see if the attrition on those features disappears with it.