If we have a token captured for a credit card and we need to update the credit card details, do we need to register a new credit card or can we update the old token?

Yes you would need to create a new token for the new card.

How do we register new credit card details without submitting a payment?

Yes you would process a payment type PA of R1.00 to check the card with the bank. This PA of R1.00 will be temporarily reserved on the customer's account and fall away automatically. We'd recommend making your customers aware of the temporary R1.00 charge.
You can follow the steps at the articles below for CopyAndPay


You can store all the info in the final getstatus payload (including the expiry date, first 6 and last 4 digits of the card) and run logic to trigger a notification to the customer to update their card when close to expiry.