nah, they can get in trouble for helping you leave to change your ticket. at least, it's not standard policy to help you out landside again just to change your flight. There are so many DMs on each flight it would just be mayhem parading everyone out landside. Immigration or customs or someone would throw a fit and I'm sure people would get in trouble for it. Once or twice would be fine but they can't do once or twice given the river of DMs they face on every flight let alone every day.

Indeed, the issue you faced is the classic PRC issue for KA/CX pax forever. You get airside, you see your plane go tech or have some other problem, and are helpless to do anything about it while another flight or two or three in your case, depart in front of you. Totally maddening. PRC govt rules won't let you swap once you're airside. I'm not even sure whose rules they are to be honest, whether its CAAC or Immigration or who...just "the government." It's a no go. Not CX/KA's fault on this one.

Standby Redemption at the Airport
 

Does anyone have experience in the above (not for an earlier flight but for a new ticket)? My predicament is that there are no redemptions available at the moment but can we try our luck at the airport?

They closed Asia Miles counter at HKG couple months ago, so I don’t think they can issue award tickets at check in counters. You can always issue your own on the spot online.