I would say that the change will be tough as Expertflyer shows only 7 more seats authorized to sell. The seatmap does not provide an accurate detail of the number of seats actually sold as not all people pre-assign seats before the day of departure. Z4 is the current PMU upgrade so there could be a chance if rev management decides to convert some of those Z seats to skysaver before the flight day. If you cant get it before the 6th then I would not count making the change.