I've been messing with the XML to see if it is possible to manually upgrade improvements. So rather than having all improvements upgraded for free when you research the corresponding tech, you would have to select an improvement, click on upgrade, and spend resources for doing this. Since it isn't possible (AFAIK) to select an individual improvement that is 'inside' a city, I've been trying to do this with a resource site. I've tried to upgrade a farm, but so far no luck. I've been able to change some of the variables of a regular farm like costs and output, and by changing it's internal name I've added a new building that has the exact same cost and effect as a farm, but can somehow be build in a city and is not restricted to fertile land (even though I didn't change the prerequisites).

So I have some questions I hope some of you can answer.

1. First of all obviously; Has anyone else been able to make a building upgradeable somehow?

2. Under the prerequisites for the farm in KingdomUnlimitedImprovements.xml it says <SupportedResourceType>FertileLand</SupportedResourceType>. I'm guessing this refers to <Type>FertileLand</Type> in CoreWorldResources.xml, and means that a farm has to be build on a resource tile with the FertileLand Type? From the Harbor improvement I've gathered that TerrainType can also be a requirement, are there others?

3. I wasn't able to find any reference to the farm in CoreWorldResources.xml, does this mean that 'the game' reads both aforementioned XML files, sees that a farm can only be build on fertile land, and then gives the fertile land tile the ability 'build farm'? Is it then possible to have multiple build options for a single resource tile, or is all of this hard coded?

4. Not very important right now, but when you change values like construction costs for one of the core buildings, in game you get for instance "25 gold, 2 materials, 25 gold, 2 materials" rather than "50 gold, 4 materials". Is there a way to change this?