In reality however there's 3 situations
The letter of the law, the intent of the law, the reality of enforcement.
@TakeshiT & @natino
You seem to going about this the wrong way.
LHS 'can be' a completely stand alone system not linked to you, your vaccine record, the internet or your travel history.
'A freind' has an old iPhone 5s that runs an older version of LHS (they don't even know what vs. it is as it's all in Chinese). That phone is a burner, with no sim card and no personal details of the owner, it's naturally not connected to the internet and has obviously never had any vaccine details (or any details at all) - It's an utterly anonymous phone.
My friends main phone has no LHS on it, but does have the E-health app and a photo of the QR code from their vax certs (as well as a few photos of a few other random QR codes).
On entering 'participating venues' my friend allows the pic of the QR code to be scanned and gets' the green light and the bing bong sound - That's all most gatekeepers want.
"Bing bong" - on ya go.....
If my friend is ever asked to scan using his LHS app (rarely) he just smiles, say's "cannot la" and walks on whilst mimicking the 'bing bong' sound.
In most scenarios this's enough.
The fact is, my friend HAS the burner phone (most of the time) so could scan the LHS 100% annoymously but chooses not to - why?
Because he can
And because that's one of the ways he learns how much he can get away with.
On the rare occasions some gatekeeper goes all super anal and insists on LHS, the burner is produced and the charade is complete, OR.....on other occasions my friend refuses that too and threats of the police are made (and ignored). On the even rarer occasions that the police are called there are another 2 options available:
1) Leave the building before they arrive - they're never quicker than 15 mins and generally take 30 mins+
2) Go to another part of said building (for my friend it's LCSD sports centres) scan the LHS with the burner (out of sight of the gatekeeper) and get on with your activity.
If and when the cops eventually turn up (even that is not a given) show them both phones, and make the anal gatekeeper lose face. This strategy has been successfully applied more than once. The old version LHS on a disconnected phone is completely legal.
But why does my friend go to all this trouble?
Well, he says because when anal people have a bad experience trying to force petty laws on others, they lose their appetite for such actions in future. And to boot, these individuals are the worst type of jobsworths who are complicit in grinding HK down. Fuck em (he adds).
Slowly chipping away at anal peoples willingness to stick to these systems in front of their colleagues is an effective way to win in HK.
So back to QR codes and LHS - Yes there is still a question about how this will work post travel when you're in the Q.period.
Today one of the gatekeepers asked my friend to scan (with his LHS) in a scenario where normally he's not asked, they were fobbed off with a "cannot la" and a smile and a "bing bong"
But maybe they're going to get back to trying to enforce b.o.t.h scanning protocols and not just be satisfied with the vaccine cert..... We'll see.
Or maybe as Shri says, the vaccine QR code will be made to turn red for those 4 days; I suspect both, but my friend knows there are always weaknesses in the system...