City names should work with the city name manager python files (plus the even manager stuff). The only problem might be the removing of the city name pop-up on city build, I am not sure if this is in python or c++.
Barbs and war maps would certainly work with only python changes.
Of the above, the barb file would be the easiest to understand and move to another mod. (the barb functions also get called from the even manager and handler files)
Firaxis could have done a better job in documenting their code (there are no comments, just intuitive function and variable names that are sometimes not that intuitive). Rhye has almost no comments for his contributions (just comments to distinguish between Rhye's and Firaxis' code).