No tips or tricks.....Rang 131 011, went through krisflyer redemption option, told them I wanted to change to X date, agent found availability, moved, done (itinerary sent and KF booking updated)
Admittedly was waiting for the "that will be an extra x KF miles" but never came. Not sure if I got lucky or what?
Of note - potentially may try change again slightly forward. The date I got today is definitely acceptable that if when I try change again that if new pricing is enforced, I won't go through with it. but will report back if success or not with moving again.