ATM keypads are an extremely expensive component that you replace as a complete module, made out of a couple of chunks of very thick stainless steel and plastic

ATM keypads are an extremely expensive component that you replace as a complete module, made out of a couple of chunks of very thick stainless steel and plastic with the PCB in the middle. They are specifically designed so that all the keys sound exactly the same, and individually tested at the manufacturer. This is something they've already thought about, back in the early 1990s.