We're working as hard as we can on the 8.10 release. We just built alpha's last night that a few of us are testing.
As for skin modification, cool. Yes, it is basically just changing bitmaps. Any designobjs that do not have matching bitmaps in their respective skin folders will fall back to Basic.
As a start I typically copy the Basic folder to my new Skin folder, and work from there.
I would suggest at least installing the Orbiter software on a windows machine, to test the UI1 variations. You should do all the variations, even if you don't use them, because others will.