When you book via TRIPS for CatA/Standby and pick dates/flights you actually listing on those specific flights and booking a 1 year validity ticket at the same time. So if your plans change or the load is high, you can go back to that ticket, cancel the listing for those dates and relist on any other flight within the validity of the ticket. You can also cancel the listing leaving it open for future use or get it refunded to you. The e-ticket will be emailed to you and looks just like any normal passenger ticket.