Any news on whether Halloween/Spooky Stuff costumes can be converted to the Spooky holiday costumes?

Do you mean as an option for your sim to dress in if you have spooky day, but it doesn't show up as the listed dress for costumes?

http://modthesims.info/download.php?t=614780

If so think this might be what you're looking for. :)

Thank you very much for sharing this little mod, LadyKyn! I was hoping a mod like this would show up. I was so disappointed when I saw the Spooky pack costumes weren't available on Spooky Day! What the heck is up with that?!? LOL Happy Simming!