How I see it is the launcher is prohibited by name now. So after reading the deactivation process, you have to weld something into the "barrel" but not completely fill it on barrels over .50 and single shots dont need the trigger welded. Hense where the idea to further customize it to only accept the sub caliber unit.
What is the legailty of a fired M72? Its a one shot throw away weapon but as I recall specifically mentioned by name in the newly prohibited list.
So is it an empty fibreglass tube or a prohibited empty weapon?
A bit of a resurrection of this thread, but a Canadian dealer has several reactivated RPG-7 launchers for sale right now (May, 2022) post-ban, and one of the 7.62 x 39 sub-caliber training rockets as well. Over $8k now. I haven't contacted them to check whether the subcal rocket can still be fired or even chambered in one of their deactivated RPGs, but perhaps there is hope!