When purchasing train tickets online and choosing to pick them up at the self-service machines I note that the same credit card must be used for pick up that was used to purchase online. Will there be a problem in the case of a credit card renewed since purchase? The number on the front remains the same, but the 3 digit security number on the back (and of course the expiry date) have changed.
Do you have the option to print them at home?
yes it could be a problem but it may work if the number is the same..What countries are you visiting. In the Uk as long as you have your reference number you can pick them up at any of the ticket counters at the major stations.
The usual advice is to keep the old credit card and use that in the machine. Nothing is booked to the credit card, it is just used to identify you. I have no idea what you do if you loose your credit card in the meantime.
The other option is, as Richard suggested, get print-at-home tickets, but these are not always offered.
Just in case, allow enough time to go to a ticket window. If it's convenient for you to pick up tickets before your actual travel date, then you'll have no worries when you arrive with luggage in tow.
If it is France, you won't be able to pick them up at a machine unless you have a PIN & chip credit card, but you can get them from a manned ticket window.
I think German Rail says you need to show the credit card used to purchase you online ticket when the conductor checks you ticket and that is doesn't matter if the card has expired, you just need it for ID. So, I would expect that might be the same thing when picking up you ticket from a Bahn automat. The credit card has already been charged, you only need it to identify yourself.