Well, thanks again to everyone, due to this thread and your advice, I've successfully made it upstairs to the international lounge.

Avoiding the transfer area to HKT, I walked up the escalator and confidently told the security clerk that I was going to the transfer desk. He nodded and all was good.

When I arrived at the lounge itself, they as usual demanded to see my outbound BP. I hesitated for a moment wondering if they'd banish me to the domestic terminal once they saw I was en route to HKT and had no business where I was, but they didn't blink an eye and waved me in.

All is good.