I've changed my SIN-MEL tickets often. They are flex fares and normally in the SGD$700-$1000 range. The change fee is standard - SGD$100

I don't think I've ever had it waived, mainly because the airport check-in staff at both SIN and MEL are 3rd party drones (ie not EK staff) and simply follow orders.

I've got no real issue, as it was a request I made and therefore I think I should pick up the cost...