There's a mod called ethnic artstyles which features new city artstyles and probably has the ones you're looking for. It has aztec-type cities for south and central america, iroqouis-type cities for native americans, egyptian cities, middle eastern cities, european cities, asian cities (maybe two kinds).
In either it, or a related mod called varietas delectat (which features all of the above) there are also viking type cities i think. VD, and maybe EA, also have things arranged in a modular format, so if you wanted to see how it works it would be easier than trying to study Rhye's.
They are just graphical mods, so if you wanted to get one of them to work in straight bts, it would be a simple matter of putting them in customassets and turning modular loading on in the config/ini.
