If that could be done to one Mauser, it could be done to another. Clown or not.
The debate is not focused on the feasibility of re-stamping a rifle to designate the caliber of the cartridge to be used on that rifle.
Any rifle can be modified to fire a cartridge that is not the cartridge that it was originally manufactured to fire.
There are some rifles that have excellent strong actions that were manufactured to fire a cartridge that isn't a very strong cartridge or the projectile is too light to be effective at longer ranges. Thus a well designed Mauser might have been manufactured to use a weaker cartridge but was then re-barreled to use a bigger, heavier, and more powerful cartridge. Of course the rifle has to be re-stamped to identify the cartridge to use in that rifle.
But this discussion has jumped the track..... The rifle that was found HIDDEN BENEATH boxes of books in the NW corner of the sixth floor was NOT stamped 7.65 MAUSER.... It was a carcano and it was stamped "caliber 6.5 " on the rear sight.