Yeah, but you’d need the algorithm. It could be a hash of some kind, and if you don’t know what kind of algorithm they’re using you can’t replicate it.

EDIT: Oh, I see what you’re saying. You mean you could simply rewrite the original card value back over it forever. That’s actually quite clever, and it would work even in case the card was completely encrypted.

Actually that means this is trivial to beat I think.