Back side of the Form 1 states:
"Important Information for Currently Registered Firearms
If this registration document evidences the current registration of the firearm described on it, please note the following information."
..."Change of Description or Address: The registrant shall notify the NFA Branch, Bureau of Alcohol, Tobacco, Firearms and Explosives, 244 Needy Road, Martinsburg, WV 25405, in writing, of any change to the description of the firearms in item 4, or any change to the address of the registrant."
Its shall, not may. Are they going to demand you go back to the original configuration? Unlikely. However, they could order you to submit a change letter. Unless you were doing something really stupid, why would they care to investigate.