Changing validation rules on advanced credit card field

Hi,

Is it possible to change the validation rule on the credit card number field? For example, the processor allows dashes and spaces along with the number and many people enter this in, so would not want to confuse the user (and potentially lose a sale) by applying too strict a validation.

Also, is there any way to prevent the credit card number from re-appearing when a user clicks the back button in their browser? Obviously this is client-side and thus not guaranteed, and am researching best practices, but if there is a standard way then great.

Thanks!
Brian