If you save an off-duty uniform, and load it into a purchased slot when you make the first edit, and never change it ever again, they apparently do work with off-duty clothes. Blackavaar's guide to colors has some posts on that I think (http://forums.startrekonline.com/sho...d.php?t=151369 - no idea where it is, in the last third/quarter or so, though).
Thanks for the link, Felderburg. : ) Fortunately, I was able to find the post in question fairly quickly; for those that don't like digging, however, it's post #285 on page 29 of the above-linked thread.
Oh, yeah: /signed -- definitely would like to see BOffs get a 2nd slot for off-duty clothing; would also like the option to freely set Captain slots to either uniform or off-duty.
But I'd really like to see purchased C-Store slots applied not just to Captains but their BOffs as well. My plan for my main captain and his BOffs was to have them receive a slight modification to their crew uniform each time they acquired a new ship. It would be nice, on those occasions when they dusted off an old ship, if they could simply activate an older costume slot rather than have to pay out energy credits to re-load the old uniform on each of them.