So you conquer a city that is a fortress and want to convert it into a town. Rather then raze and rebuild it would be nice if there was an option to initiate a construction project to convert it.
How would you suggest such a thing work from a mechanical perspective?
Method 1:
I think it should put the city into "conversion mode" which:
1. Deletes all current build orders.
2. Demolish all specialized buildings.
3. Cooldown of 1 turn per city level.
4. Open the new specialization choosing menu but NOT give you the bonuses you choose right away. Rather, the specialized buildings (the ones that give the city its special bonuses like the oracle or farmers market, etc) would be queued (And nothing else but them can be queued).
5. When last city upgrade building is built, resume normal operations.
Method 2:
An alternative and simpler method is to just calculate out a cost based on city level and "construct" a "city conversion". When conversion is finished scrap all specialty structures as well as city level bonus giving structures and activate normal city levelup interface.