Let's clear it up.
Changing from AMM-AUH-SYD in J to F = no change fee (upgrading class of service).
Changing AMM-AUH-SYD to AUH-SYD = no change fee (dropping segment in same region, same award type, same mileage).
Combining the above, changing AMM-AUH-SYD in J to AUH-SYD in F = no change fee. (One could theoretically also change AMM-AUH-SYD-CNS in J to AUH-SYD-CNS in F and then change that to AUH-MEL-CNS and then change that to AUH-MEL, all without fee.)
Changing AUH-SYD to DXB-SYD = change fee (changing origin and changing award type).
Changing LHR-DXB-SYD to DXB-SYD = change fee (changing award type and mileage requirements).