Let's try a slightly more complicated scenario
One PNR - open jaw
CMB-HKG-MEL//PER-HKG-CMB y->PEY upgrade HKG-MEL (no PEY CMB-HKG)
If I upgrade PER-HKG (again no PEY HKG-CMB) Y->PEY would it be worthwhile to email MPC as the upgrade category (HKG-Australia) is the same for both legs.
Thanks for your wandering
Fred