What would that achieve? If you're late to the blockchain (or really any other distribution channel, like https://truetimestamp.org/ or something like this) your timestamp is greater than original and you own nothing. I don't really know how selling 2nd place works with NFTs but I assume you only can get it from 1st place owner (he has to sign it with his private key), so the scheme is solid. You cannot change a pixel and claim something.

The only problem I see is how the 1st buyer knows the seller is the artist not some random dude who changed 1 pixel (or even didnt). You actually cannot reliably sell something that has been published before cause everyone and their mom can claim ownership before 1st token.

Or indeed changing some irrelevant metadata that would have precisely no impact on what's rendered on the screen.

Well, physical art reproductions are high quality already (I have some Van Gogh canvas prints I bought for like 50$ a piece on my walls). So you can't really say traditional art images are scarce too.

The thing is whoever is owns the original in some sense, even if you eventually cannot discern it with a microscope.