A quick update after my 55 minutes call with Qantas.
Here's my current itinerary
KUL - NRT MH88
HND - GMP JL91
ICN - KUL MH39

A few things I trying to accomplish,
1. Change from MH88 to MH70 and dates
2. Change from MH39 to MH67 and dates
3. Save the 2 surface segment between NRT-HND, and GMP-INC, by changing JL91 (HND-GMP) to JL5201 (NRT-ICN) (code share by Korean Air, found it in JL homepage)
4. If 1 is done, book myself under MH70 and my wife under QR5398, it's the same flight, but market under QR

Outcome,
1 & 2 - no problem, initially the agent said I need to pay fare difference. I said ok, pls check. After 15 minutes, she said, no need to pay.
3. She cant find it in Qantas system, thus cant change to this
4. She can split one booking to multiple (this was what chan1108 asked), so if QR5398 exist in Qantas system, then she would change for me. But same with 3, she cant find it. Thus no change.

Would like to get some advice, 3 & 4 sounds logic to me, should I give up or call with again or try with twitter team?