I added a friend's tower enfield 577 musket to my SGC with a simple email a few years ago. I am now having it taken off and reverted back to section 58 Antique. I sent an email to that effect a couple of months ago. Should be simple and it certainly used to be, but I have an FEO coming out on Wednesday to check that it can revert. (That and my FAC, SGC and exp ticket renewal). It seems that they are becoming more careful about what becomes antique. I'll let you know how it goes!