Just wanted to follow up here with what I found so far... When I clicked the "Save" button that appears when you edit the morph, I originally thought that it only saved in Carrara format. I looked more closely (always a good tip...) and found that it would also save in OBJ format. I saved in that format, and imported the OBJ into another modeler. Only the morph area came in. I edited it, saved it back to an OBJ file, used the Load button in Carrara to bring in the morph, and it worked.

I'm not sure if any of the OBJ import/export options are better or worse for this kind of thing, I'll have to do more experimenting. Initially, I used all the default options.

When I made the selection to define the morph area, I selected faces, edges, and vertices all at the same time, which may make a difference in the OBJ file that gets output.

Also, when editing the morph, I didn't modify any of the edges or vertices in the morph area that are shared with faces of the object that are not in the morph area; dunno if that would make it hiccup or not.

Still going to play with it, but this is more or less workable.

Wouldn't say no to being able to dynamically link to Hexagon in the future, or to have any other improvements in the pipeline, of course.