advice for the following situation

I booked a flight using points from MEL-LHR in business on QF29 however Qantas canceled the flight on that date and changed my flight to the earlier Qantas flight 9, however I have an appointment for the day and thus thats why I choose the QF29 departure as it leaves at midnight giving me plenty of time to get the airport.

Would Qantas be willing to rebook on the Cathay flight that leaves at 01:05am via HKG, or even the following day on Qantas

Searching the Qantas website there is no actual award availability on the following day in business, would Qantas create a seat for this day for me I am Qantas Platinum if that would help.

I thought I would ask here if anyone has had a similar situation and what the result was before calling Qantas to see what they could do for me

any advice greatly appreciated

For an involuntary reroute (which this is), QF has a legal obligation to get you there using any airline for similar routing. They are much happier using QF (and you would be too, QF J is better than CX J these days). So you could insist on the CX flight, or QF will use a seat on any QF flight (even if no award inventory). Note that this is different than a voluntary reroute (e.g. if you were late and missed your original flight), in which case award inventory must exist (and might be created for WP at the discretion of yield management).

Expect to push really hard to get on the CX flight, especially in the premium cabins. CX and QF don't really get along when it comes to award inventory. CX don't really care you're a QF Platinum.

I suspect they'd offer you next day's QF flight before having to go to CX.

I would prefer going on the qantas flights anyway so hopefully they are at least accommodating enough to change the day, although I am biased by going via HKG for a couple of reasons firstly gets in to London at a nice time, chance of still only being sold as a three class flight so might get lucky and travel in a first class seat with Business service

so I will see what happens when I call qantas tomorrow and let you know how it all goes