Thanks for that Mark. Might be a useful bit of information to put on the P11 site:
http://www.platform11.org/passenger_info/ticketing.php
Now of course what would be really useful is if I could book a seat on the Cork train down, and then change my booking so that my ticket is valid on the Millstreet service coming back up, and book a seat on the Mallow-Dublin leg.
But I'm not sure I have the energy for dealing with the soviet-style shenanigans at Abbey Street today!