Would like to seek your experience in changing award redemption for my booking.

My multi carrier award was issued last month involving QF, AA, IB and QR with 5 flights.

It has recently come to my attention that the last sector by QR (originally economy) has business availability if I change to a later flight on the same route.

I called the hotline and the first operator said change of reward flights operated by QR is not allowed because QR does not allow keeping the existing seat while holding another flight (because BA needs to hold the seat first and wait for a few days to calculate the tax).

The second operator was willing to help, and said that the business class seat on an alternate QR flight was reserved pending tax calculation. However I waited for 3 days without update, and I noted that seats availability on ba.com remains the same (i.e. no seat was held)

I called again and the third operator replied that some partners just do not allow BA to hold seats for longer than designated period, and it’s likely that QR released the seat on the alternate flight. He suggested issuing another new set of multi carrier award redemption, and cancel the first redemption afterwards. However this is not possible because QF does not have any availability shown on BA.com

I really want to fly on QR business instead of economy. Any experience/suggestions on how to work with BA on this?