I agree, but the wording said to dispose of or alter.I haven’t read the 200+ pages, just a quick glance. Can’t see why you would have to destroy the brace as it itself is not illegal.
3. Permanently remove and dispose of, or alter, the “stabilizing brace” such that it cannot be reattached, thereby removingthe weapon from regulation as a “firearm” under the NFA. The Department recognizes that the removal of a “stabilizing brace” from a firearm that was originally received as a “short-barreled rifle” results in the production of a “weapon made from a rifle,” as defined by the NFA. However,theDepartmentin its enforcement discretion will allow persons to reconfigure the firearm to a pistol by [INSERT DATE 120 DAYS AFTER DATE OF PUBLICATION IN THE FEDERAL REGISTER] and will not require the registration of these firearms as a “weapon made from a rifle.”
I would also think modifying the buffer tube would be like modifying a lower to not accept a short barrel upper.