How So? Not true.
For example the BRS-99 that could be changed to NR with a barrel change.
The CZ scorpion evo carbines that are being brought into the country which include the restricted barrel as well.
The 18" barrels which were made so the Bushmaster ACR 's could be reclassified as NR
I am sure there are other examples; these are just a quick few I thought of
CV/ Comercial variants can be converted. "Pistols,"again from my understanding of law, will and not be able to be converted to a NR status/firearm.
If I am wrong please correct me!