My suggestion:

Using a search function, find all files in the Data and subdirectories that contain the reference for a particular building you want to make available. Go through each instance and record what the links are to other files, such as graphics, and the faction it currently exists in. You will then know exactly what you have to do to add it to the new faction, just create new entries and links exactly as you find them but with the new faction.

Be forewarned, many links exist so you will be spending a lot of time tracking down all the little things you will have to change to make it happen.