I booked the following:

SQ861 HKG-SIN Suites
SQ221 SIN-SYD Suites

The issue I have with the above itinerary is that I only have a 1 hour connection in SIN. I don't want to take SQ231 since the service will be somewhat abbreviated with the 00:45 departure.

I actually want to have a long layover, and would like to take SQ865 the day before (there is confirmed Suites availability,) which arrives into SIN at 22:40. Leaving on SQ221 the next day at 20:15 would put the connection at just about 22 hours. Only thing is the site doesn't give me this as an option for HKG-SYD.

Would I have luck getting them to change just the HKG-SIN segment over to 865? I've heard they're somewhat fickle with these routings that don't show up online for a city pair.