Two naive answers.
Look at some aircraft histories while they were still in service.
"Mk V upgraded to Mk VIII. Re-engined with the new Tigerskin engine, while retaining the original Mk VIII airframe.After a ground collision, the aircraft was returned to service using the wings from SU 159 (squared-off wingtips)".
Aircraft are repaired, overhauled, reskinned, updated, etc. all through their lives. Even before becoming a "historical" aircraft, one can argue about how "original" it is.
I go with Kitbag too. If it looks like a Spitfire, smells like a Spitfire, roars like a Spitfire and flies like a Spitfire, to me it IS a Spitfire.
As to the new Me262s, if even Messerschmitt has agreed to accord them five new Werke Nummer, I no longer would call them replicas, just five more aircraft of the same type, with a few updates and improvements (mostly the engines), so they would be acceptable to fly sixty-plus years on.
There are the "historians" and those who like to see an ancient plane fly again, even if it's a full replica.
Sadly the two will never fully meet....