A building with a lower level is always replaced by a higher-level building. When building a map in map editing mode and placing my buildings, will a lower level building be replaced by a building with a higher level? Do the buildings I place have the same rules as those of randomly generated cities?
A lower level building can be replaced automatically by a higher level building. This happens when the city needs more housing, I believe. Then, if it cant find a spot to put a new building, it will find a building inside the city which it will replace with a higher level building.
I believe that all buildings are threated equal, so the buildings you manually place will be threated just like the automatically placed buildings.
There is a feature "disable growth", that I think will prevent the replacement from happening, although Im unsure of how it works.
"Disable growth" does exactly what it says, the city will simply stop growing, this way there will never have need to increase or upgrade buildings.
There is also a tool to buy buildings. Normal city buildings are unowned, i.e. their window has an orange frame. Owned buildings are never upgraded. So when you buy a building, this is protected from further replacement.