I'm looking at booking XXX - DUB - IAD on a Smart Fare, but don't know when my return flight is going to be yet. Purchasing the roundtrip is cheaper than purchasing two separate one ways. Is it possible to book the roundtrip, and then after the outbound flights are flown, refund the return part of the ticket to a voucher? Or do I need to change the dates of the return portion (within 1 year of the original booking)?