As others have said it's perfectly doable to go landside and back through at HKG... but I am slightly confused about your reference to checking out the "rapid transfer system". Just in case you were referring there to the automated people mover (similar to the LHR T5 "transit" that shuttles between T5ABC), that's airside. Unless of course you wanted to try out the branch of the APM which shuttles people who have checked in at HKG T2 to the main terminal after clearing immigration and security.