There's no mystery where the line goes. Legally, everything but the data plate with the construction number are spare parts, and can be replaced without making the aircraft another individual!!
This sometimes can give confusions in listings of warbirds. Example, on august 13, 1998, a SNJ-5C crashed
near Winlock, Washington, in USA. This was officially the american built 41-16621 in all paperwork, BUT, the entire airplane was in fact a canadian built Harvard IIb, with the real id being 42-12318, formely FE 831 with RCAF, and 16010 with the Swedish Air Force!
So why did it crash as a SNJ-5
? Well, canadian built Harvards have never been certified for commercial flying in US. They are legal for private flying only. Only reason is that no one have tried to certify a canadian Harvard IIb yet. Who ever does it will have no problems doing it, but will have to pay the initial cost to FAA. All the following aircraft will be for free. This aircraft came from a museum in Sweden. The new owner had plans to do some commercial flying in USA, only to discover the truth about canadian Harvards. So somewhere he found a data plate for a SNJ-5. By legal terms, he did not switch the data plate in the airplane, he simply put a lot of spare parts around the new data plate!! Perfectly legal
! I've seen this done with other airplanes as well.
CAA or FAA doesn't matter. The rules are the same!