Could you attach your save file to that post, please? I don't have that DLC and have no idea how those would differ from normal vehicles. I'm pretty sure i didn't have trouble editing with the save file Las0mbra sent me earlier, which had the Ultor Intercepter DLC vehicle in it.
I've also added a warning right under the Instructions header that you should always back up save files. Thank you for reminding me, and for being smart enough to do it without being reminded yourself. Whew!