If it's an entirely separate reservation made through CX HK then I'm sure there wouldn't be a problem. A OWE can be twenty separate PNRs if that's what it takes to get the flights (most of mine have had 4 or 5 PNRs associated with them during their lifetime).

I would never ticket a waitlist - I'd ticket an open segment (in A not D - never get an AONEx coupon issued in D if there is ever A on that segment, it's a bugger to get into A if the coupon says D) and then make a separate reservation. I see that CX410 is 3 class that day, so I'd be pushing for A on that (even though it is showing F4A0 at the moment in EF).