That is certainly how things worked before covid. It was fairly routine to obtain your boarding pass at the flight connection counters at T2/T3 if the airline could not issue it at origin. Even without onward ticket, you could even take the airside bus from T5 to T2 to exit at T2 rather than T5. Whether this is still true in covid times I have no idea.

You may want to consider buying a ticket on the 6H15 and a second ticket as insurance policy on the 11H50. From memory, the early morning HKG flight is the very first so, if you are in F, you should be able to get to immigration before queues build up even if you have to go landside. OTOH, there is always the potential problem of being parked at the B or C satellites, which will slow your reaching the main terminal and may allow others on the flight to overtake you.