So I import the model + the genitals as the documentation of the script says; then I select the genitals (in Blender) and make a second import this time importing only the morphs of the 3rd party genitals; after that I merge (in Blender) the imported model mesh and the mesh of the genitals and they should keep the morphs, right?
Yes, that’s the idea. By default the shapekeys are driven by rig properties, so you should merge all rigs first. The driving properties turn up in the Custom Morphs panel with the rig is selected.
Importing custom morphs is by no means limited to genitals - it works in the same way for clothes, hair, or the character mesh itself, if you want to import something else than the standard facial expressions. However, most meshes cannot be merged with the character with the Merge Anatomy button; the mesh must be a “grafted item”, which is some extra inforrmation included in the duf file.
Must I first export those morphs from Daz as the original model had to be exported?
No, you load the duf/dsf files directly from the morphs directory belonging to the selected mesh. The file selector should open in the right morphs directory, and all relevant morphs should be found in subdirectories.
However, if there are several morph directories belonging to this mesh, starting from different root directories (which you set in the Settings panel), the plugin will choose one of these.
If I make the poses in Daz and morph the genitals there to correspond to the poses then when I import the model together with the genitals to blender will the imported genitals keep the morphs (which are pre-made in Daz)?
No. All morphs are baked to the character mesh.
PS. I have version 1.3 installed. Is there a new version?
Only the unstable development version. However, it contains some important bug fixes, in particular for cycles materials, so I would recommend that if you can live with that things change a bit (and occasionally become broken).