I've combined some primitives into a new Prop.  I am saving as an OBJ but unfortunately I am ending up with all the mat goups originally assigned to the primitive props.
Is there a program or way to DELETE unwanted MATERIALS from an OBJ?  I've tried editing the MTLs out of the obj but it corrupts the file.  It would be nice if you could do this in BLENDER. Maybe you can. But I am not sure how.

Thoughts?

Open up the .obj file in a text editor, find usemtl at the head of the f lines, rename this to usemtl  "your material". Delete all other instances of usemtl and "name".You will now have one material named "your material". Similarly, if you have multiple groups (g), you can use the same process to quickly create a single group encompassing the object. Never ran into any file corruption using this method, .obj files aren't very labyrinthine.

I don't use Blender but you can easily edit materials and groups I'm sure. In wings3D I would import the object, right click, select material, create material, select object, in the outliner right click material, assign to selection. This overwrites the prior materials with the new, single material.

Archaic morph target trick...

Open your morph target in text editor, copy all lines starting with v (vertex). select all text. Delete. Paste. Save as "morph" .obj. load morph target on figure. What you have created is vertex only obj morph file which simply moves vertices and does not include the mesh. The file is very light and handy for sharing original custom morphs without utilizing INJ.

More .obj trimming tricks... open .obj file in text editor, select all lines beginning with vn, delete. Poser assigns normals upon import, the vn lines (vertex normal) are extraneous.