How to make building destroyable?

[madtomic]

Buildings that change strat-map appearance (palace, roads, farms, walls) cannot be destroyed without causing a bug.

Once a city gets to a level, there is no way in making decrease in level or change the cultural appearance of the town while keeping it the same level.

If your towns are Large Towns, get them to 6,000 population and you'll be able to upgrade them to Minor City.

All the towns are large but some towns I had rereach the pop. of 6,000 and no option to upgrade to minor city because it has already had the holds of that level in the town before I conqured it. I guess the next step is next city level at 12,000?