IMHO, they are either going to have a problem with you changing the award ticket or not. Here are the date change conditions for domestic award tickets from ANA. Wether this information is applicable to the Virgin ticket or not seems to be the only real hurdle you'll have so long as you are 4 days out.


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Changes on reserved flight date

(Sectors and passenger's name cannot be changed).
If you wish to change your reserved flight, reservation change must be made 4 days prior to the new departure date (not including the day of departure). However, the change must be made prior to the originally reserved flight. Open sector is not accepted. Confirmed reservation must be required. Please contact ANA Mileage Club Award Reservation Desk for the reservation changes. However, when a seat is available on the same sector fight prior to the reserved flight on the same day at the airport, you may board that flight. Open ticket issue is not permitted. The entire itinerary must be reserved. Please contact the ANA Mileage Club Award Reservation Desk for reservation changes. When changing resevations on the date of travel, please note that you can board the previous flight of the same sector on which you have made reservations if there are seats available on arrival at the airport.

From this page http://www.ana.co.jp/amc_e/guide/tokuten/muryou_jp.html