answer:I’m not a banker, so don’t count this as a totally authoritative answer, but I would think that punching a hole for a keyring would NOT in any way invalidate a card. Why would it? As you said, don’t damage the magnetic strip, but popping a hole in the bottom (under the raised letters) isn’t going to harm anything. Try it!. And of course almost every credit card issuer has a website that lets you do a card reorder in case it is a problem.