How would anyone, even EBMM know the neck is not the original?
The neck, and body are itemised separately on the factory documents.
If for example, the neck got damaged at some point in the future, in order to get a replacement from EBMM you have to return the original neck.
If the one you return is not the one listed for that instrument, it's going to get complicated.
Even if there is never that kind of problem, owners are encouraged to register their instruments with EBMM - and anyone can retrieve an instruments serial number from the EBMM database - which reveals a number of details about the instrument, including the official "birthday" of the instrument.
The "birthday" is the date stamped on the neck heel, not the date written on the control plate (or neck pocket).
There's any number of ways you might discover that discrepancy, whether curiosity, fitting a shim etc.
I think the vast majority of people would be livid, if they discovered that somebody had previously tried out their supposedly brand new instrument, for
30 days at home, and swapped a major component out.
Besides it being morally wrong, it's almost certainly illegal.
You wouldn't dream of taking a car off the lot, for a test drive, and en route swapping the wheels for those of a second car that your trying (even if it were the same dealer).
Swapping the strings would be like swapping the wheels - swapping necks is like switching out engines.