Although I'm not a MA resident, it appears to be true. I read a little bit about it after reading this post. I'm not certain, but if I read correctly, a pre-'94 built rifle would not need this mod, but you'd better check for sure.
I did find this about the attachment method:
"One example of an ATF approved method...
DEPARTMENT OF THE TREASURY
Bureau of Alcohol, Tobacco and Firearms
Washington, D.C. 20226
JUN 18 1998 F:FPD:FTB:RAT
Dear Mr. :
This refers to your letter of March 31, 1998, in which you ask
about permanently attaching a muzzle device to various firearms.
A muzzle device, such as a muzzle brake or barrel extension, which
is attached to a barrel by means of welding or high temperature
silver solder having a melting point of at least 1,100 degrees
Fahrenheit, is considered to be part of the barrel for purposes of
measurement. A seam weld extending at least one-half the
circumference of the barrel or four equidistant tack welds around
the circumference of the barrel are adequate for this purpose.
A firearm having a muzzle brake, cap, or barrel extension
permanently attached by those same methods to cover the threads on a barrel, would not be considered to have a threaded muzzle.
Please note, however, that any muzzle device or barrel extension
which functions as a flash suppressor or grenade launcher would
still constitute one of the qualifying features of a semiautomatic
assault weapon as that term is defined in 18 U.S.C. section
921(a)(30(B). Industrial adhesive products are not an acceptable
method for permanently attaching a muzzle device."
Lord, I pray this form of lunacy doesn't become nationwide after November....