I’m not sure you can but think it’s a bit grey… I suspect that’s why the ad is “looking for the owner “ in order to cover themselves
Looked into this a while back, it's rife in the MK1 and MK2 RS world. In short, no, to the best of my knowledge and digging, it's not illegal. Morally reprehensible perhaps? However, look at it another way. Watching a chap "restoring" WW2 warbirds. Not one original part other then perhaps the build plate/engine plate etc. This "restored" aircraft then becomes the original one with wartime provenace.