I will be staying in the new Rydges at SYD International terminal before flying Qantas domestic next morning.

I will be staying in the new Rydges at SYD International terminal before flying Qantas domestic next morning. As a QFF Platinum can I get the free Qantas terminal transfer bus?

You should be able to do so. I've passed through the security checkpoint and have had them scan my QFF card before boarding the bus, though you should be able to check-in at transfer desks too.

Depending on the time of your domestic flight there is a free shuttle bus that will operate for guests between the hotel and domestic airport from 6am-11pm daily.

Stayed there a coupe of weeks ago..the free bus leaves every half hourat the front of the hotel.Is only a mini bus but gets you there,you could also take the train for $5.

If you are going International -> Domestic its easy, just walk in, hcek in or show them your BP/FF card go through security.  Im not sure about the other way though...