No but I think there should be a way to keep a newly conquered city under control without killing everybody or demolishing most of the buildings!

Wouldn't be a good idea if a Type IV goverment made it easier to control the city? Citizens should be happier, since they accually keep their previous way of goverment.

I think that is what Alexander the Great did. He kept the existing satraps in most of the cities (Babylonia, Sardis, Susa etc) he conquered, placed a small garrison and he was able to move on without having to destroy every single city.