LoadT, on ID travel? With CX or other airline tickets? Full fare is a given, that is not the point of the thread.
CX is giving no guidance on transiting with CX ID tickets. The best I can guess is that LLLQNH has the answer, as once you are through immigration on landslide you can go upstairs to departures and check in at CX staff travel. Somehow you need to let the health department know that, sensibly, you do not wish to stay in HKG and will not provide the compulsory tests over the next few days. Otherwise the state police will come to the address you have given on the arrival form and hammer on the door.