Booked before devaluation. Changes made after devaluation.
PVG > SIN > MEL
1st leg 27 June changed to 3 August
2nd leg remain same on 18 Oct
25 USD only. No additional miles.
To my understanding, additional miles are required only if you change your origin or destination (reissue of ticket). Changing of time or flights on the same route will not trigger a reissue of ticket.