Originally Posted by
paul4471
... in HKG for example on long transits you can arrive from int'l destination (probably not possible to arrive from a domestic location in HKG - side issue?), transit up to the lounge (drop off carry on's etc), then get a pass from the lounge allowing you back downstairs to the incoming immigration area (you just walk back through a side lane of the transit point), head off to Central for the day on the express and then back through outgoing immigration. Done it plenty of times - the Wing is great but there's only so much time I desire to spend in any lounge.
Have you ever read what the pass says? It is "access to the transit desk". So they use the fiction that you are doing this (going through security in reverse) not because you want to exit the airport -- that is not allowed, it is a security breach to leave your things at the airport while you leave -- but that you are needing some help with your ticket. Never mind that the lounge staff are far better able to provide this ticketing help than the transit desk. An interesting dance with the bureaucracy.
All airports do have a specific procedure for pax to leave departures. As mentioned it is common and generally easy. As for validity of your ticket, it remains valid and in original state even after it is pulled. The flight may not operate even after it has left the gate, for example, for lots of reasons (weather, mechanical, illness, ...). Imagine the chaos if airlines could not routinely handle tickets of pax who have boarded the plane but not flown (so need to rebook that same sector). Not sure about LCCs, but all IATA member airlines can handle this smoothly.