I am a Blender guy, so have no idea about Hexagon (and don't know if anyone uses Hexagon at all), but the mesh is a mesh no matter the software and I know many Daz store artists use Blender to make morphs for their Daz products, so there it is:
Every model , for example Genesis 3 Female, uses a mesh. You must not change the number of the polygons, edges or vertices because if you make even the smallest change it will not be genesis 3 Female anymore. What you can do is the move a group of vertices, edges and polygons - this is a morph explained very simplistic. If this "move" is not in the head, it is "body morph" (not sure about the 2 parts of the neck - are they body or head, should be body). So you record the starting and the end position of the moved vertices and put a slider from 0 to 100 (simplistic again). About the clothing - I think morphs of the professionally made clothing are made in the similar way, but if you make clothing for your own need you can use "Transfer Utility" of Daz to auto-transfer *some* morphs to the clothing from from the human body.
Here are 2 tutorials:
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