In my personal experience, staff at HKG will hard time you if you ask for a return boarding pass on a turnaround. They said they can't access the system at outports if the destination is HKG itself. Or maybe mine was just too faraway, might be easier for places like TPE I don't know. Best is if you can get a mobile boarding pass. If you wanna do ex-Japan then I guess you will be on 160 stock so that won't be a problem.