IPlural pointed me in the direction of a newsreader called Agent, and I'm so far enjoying it..... Thanx to John, and Agent, I have your answer.....................

Make backups of both skins folders, or make work copies of the original
skins under another folder.
Navigate to the folder of the skin you want to change to a subskin.
Change the *.UIS file to *.SSS.
Make sure that there are NO images that share the same name if they are
not identical.
Move all of the folder's files to the new folder. Open the *.SSS file
and update the paths to the new location.
Create a *.SSD file or edit it if it already exist. Add referances to
the various skins (use any preexisting one, from any compoune skin, as a
template)
You can also use skinstudio, but I personaly never done it

Alain

It may be a bit of a hassle to do it this way, but it works.