No way to delete any unwanted structures or buildings.

only way to add another one (if so desired) When all existing spots are taken is to increase the level of the province which in turn will open another spot.

I think there is one way, but it's extremely time consuming and costly.

Basically you set up with a friend, for them to attack the province over and over.

You defend with but a single troop. They attack with several doing a lot of damage.

Eventually, if lucky, you may see whole buildings get destroyed.

You see, I had it happen in a game once where a building I had built and wanted to keep changed hands like 6 or 7 times, and at the end when I finally got it back I was down a University and a Barracks.

But this took many battles and the province changing hand many times.

In the same amount of time, one could easily build a province larger and build the building you want. You also have no control over which other buildings might get damaged or destroyed in the process.

Maybe a future upgrade to the game here. For gold no resources back? An upgrade option on troops would be great as well. Killing them off so one can replace...but then i guess that keeps the fights going.

That probably wouldn't get implemented, as the gold usage for that purpose would likely far-exceed what is generally considered fair play for game balancing. But, you never know....they might do it.

There is an easier way to get rid of the building...along the lines of @marzohnnes post. Just piss off your neighbor on the other side of that province. It need not be a friend. And if you attack an AI, it'll definitely come at you, so pick an AI (or human) on the opposite side of that (or those) province(s) which has/have the undesired buildings.

Of course, then you are still facing the time and resources lost to perfect that province.

In the long-run, you'll learn to accept whatever you get and just conquer more provinces to get what you do want (e.g., a province with high-level mercenary camps or all economics, etc.)

Perfectionism in this game is nearly impossible to achieve, especially in light of competing human players whom enjoy knocking down your freshly-made sand castle.