If you change a DC reward prior to it being ticketed (any carrier) then they will normally do this free, sometimes a bit of gentle persuasion is required. Its worth noting that the fee is per pax, not per booking i.e. 4 x pax on 1 reservation = £80 fee. Changes can be made up to day of travel but no changes on return trip are permitted once travel has commenced if the booking is a return trip. One way redemptions are of course the preference of DC members to avoid this.