I am aiming for a Global Template where the mapped controls can be inserted into any new document, not based on a particular template or pre-built with additional XML. I am looking at being able to do this entirely within the Word interface once it is set up with no additional work in XML.
See the attached template, which when used as a Global Template, allows insertion of the mapped content controls into
any document. Again, these are repurposed Document Property Content Controls. (I may make additional changes to this. Here is a
live link.)
In thinking about this, it occurs to me that if the form developer's Normal Template were to contain the XML mapping of custom Content Controls, the mapping would be present in new documents.
I can see the possibility of having an alternative blank development template that had the mapping being used. It would also have the building blocks and should work much the same without being limited to the document property content controls. One would start new templates based on that blank for distribution. I think this is along the lines you are talking about without having to do any XML modification of new documents. That template could also be shared.
(P.S. I still like using mail merge for this, though. I am referring back to the original question.)