2 years later, and it's not exactly what you want, but you can combine these two mods:
- https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3376816036
- https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3470284733

First one allows you to only have one city in your starting region.
The other one forbids all cities to build roads, so if you don't build any, cities won't grow.

This also mean that if you building entire cities, they will not grow back (unless you place a road close enough to their origin.

thanks man! actually somebody made the mod days after i posted and than eventually it was just deleted unsure why