You might try this ...

Use the "Grouping Tool" and ...

1. Create a "New Prop" from the good top part (geometry) for the top half of the head
   ........(call it "HeadT")

2. Create another "New Prop" from the good bottom part (geometry) for the bottom half of the head
   ........(call it "HeadB")

3. Make sure that the "HeadT" and the "HeadB" objects are positioned*correctly and then ...

4. Export both "HeadT" and "HeadB" as a Wavefront OBJect to a file ... "NewHead.obj"
   (make sure to check "Include groups..." or you will lose this info)

5. Import "NewHead" back into Poser making sure to UNcheck ALL options (except "Weld ...")
   It is now a single object and if it looks good ...

6. Select the head on your figure and ... [menu] "Object" >>> "Load Morph Target" and ...

7. Walla !!!

Warning !!! .... The Morph Target (geometry) MUST HAVE the same number of vertexes as the head or you will get an error and the MT will not load.
If you encounter this problem, you may need to go back and add (or subtract) one or more vertices to (or from) "HeadT" and/or "HeadB" and then re- xport to "NewHead" ... etc.

cheers,
dr geep
;=]
**

• IMPORTANT !!! -** the vertexes in the geometry between "HeadT" and "HeadB" need to match EXACTLY and then check  "Weld identical vertices" in the "Import" Options.

Remember ... "With Poser, all things are possible, and poseable!"

cheers,

dr geep ... :o]

edited 10/5/2019