Hi @halfcoupler,
Unfortunately, exporting more than one object's mapping is not supported yet. Currently, you can export the whole mapping or a mapping for just one object.
The only way to merge two mappings with more than one object is by hand. You can open the two XMLs and copy the part that you are interested in into the other XML. Save it, and when imported to Vectorworks, it will load all of the included objects from that file.
You can send me the two XMLs and write me which objects you want to be in the mapping, and I can do it for you.
You can also create an Enhancement request for your case.
Kind Regards,
Nick