I have a HK94 that I am going to file a form 1 on .I want to have it remarked to a MP5 and my understanding is that you cannot remark a NFA firearm. Do I have to remarked it before the form1 is returned approved or before the short barrel is in place? The 2 smiths that I am thinking about doing this are both closed for the holidays. I will also have my info engraved at the same time .Thanks Brian