I emailed the RCMP firearms lab asking about the legalities of installing a restricted length barrel on a non restricted unregistered firearm and that is what I was told. This should be no different and I wouldn't go trying to make things any more complicated than it needs to be. As long as you initiate the registration process as soon as is reasonably possible using a certified firearms verifier I can't imagine how or why they would try to charge you with anything.
Get caught at the range with it and I'm sure things will go badly for you in a hurry.
If you're worried about it I would contact them directly and ask them. Other than that Suputin is probably the best source of info since he has a firearms manufacturing license.
So in other words you don't know and passed along something you heard from somebody else at sometime. In the example you mentioned above the section of law has been provided and if you change the class of a you have to report it within 30 days to the registrar. That is clear but considering this object isn't a firearm until it is that section doesn't apply or I think you would have trouble arguing it applies.


















































