So regardless of wether its a new building or not, what you want to do is have a building to be temporary out of a players control? ( not being able to destroy / capture) ? And it cant be a mod, in that it must come with the map itself? Did i understand that right?

I'm fairly certain the only way to do this would by setting up a script trough the mapeditor. For example create a zone around said building with particular conditions that turns the building to a 3rd party state or neutral side and when other conditions are met return the building back into player control. A script would come with the map and not be a mod. I must say i never really expored the battle editor in depth, because its somewhat a complex menu inside the editor.I know you are thinking if its a 3rd neutral state they can still be destroyed, but it could be a non playable party, that is allied,and hence wouldnt be able to be destroyed or called up on when wanted and removed when needed. It probably would be somewhat complex to setup such script, but it would be the first thing i'd look at if i wanted to do such thing.

I'm not trying to be funny. I really would like to play a map you design. I play every map I can get my hands on. You're all theory in a lot of topics. We've yet to see it in practice. There are editor manuals available as well as already existing maps to modify and learn. All talk and no play makes Jack a dull boy. 

But tell me, how do you propose to manipulate the game files so that villages destroyed using scorched earth tactics during a tactical retreat would be rebuild later in the game after a successful counterattack? And how much time are you willing to invest personally in achieving that?