If a supporter goes to the website and makes a donation without signing in, the system will try to match the supporter's email provided for the donation to an existing account. If a match is found, the payment details on file will be updated to the new information, but will not any recurring donations already in place.
If a supporter signs in first and updates the credit card before making a donation, they can uncheck the box asking if they want to update all recurring donations. Once unchecked, the card on file will be the new card they used for the one-time donation and the recurring donations will stay on the original card.
If a supporter uses a different email address than their account is under, should they have a secondary email address, a second account will be created and the credit card information will be added to that new account, leaving the original account alone. As this circumvents the replacement of the current card on file, please note that if a supporter does this, there could be potential confusion moving forward as to which account they want to use.