Originally Posted by Cambo

What I would do is, keep low profile, contact the CX desk (through the means, they contacted you with the proposal, later by email) and find out, what the reason for the change is, it gives the background info for your negotiation. Booking a single leg on (non-OW) LH-J a month out does cost CX probably a fortune, so, if they could do different, they might be willing, etc.

So, IF you have a proposal ready which will be cheaper for CX, IE, own metal, provided not booked full, CX might be willing to consider your proposal. Explain about your final destination (on your own account for FRA-LHR), and give the suggestion, they book you direct HKG-LHR (or maybe MAN), assuming this does connect.

Use EF and matrix to find out the factual flights and seat availability. Since it is CX doing the itinerary change, restrictions around married segments and booking classes are largely not relevant, CX needs a solution, be it the cheapest one for CX. Forget about "points/miles" for your original leg FRA-LHR, these short distances bring hardly any benefit.

Deal with these things at a low profile, understanding their reasons and reasoning, and they will copy back on this, it usually works the best. Don't insist on getting a solution right away, a couple of days more, might give time to settle. Doing so, did bring me redemption tickets between EU and Asia in J (with transit in HKG), 6+ months out, which is generally considered "impossible", though, I got these without a hitch (granted, I am DM, with the 2023 extension already "earned").

Regarding the lounge access, flying CX would give you the MH lounge in KUL and "The Pier" in HKG, not that bad, to put it mildly. LH metal with a currently unknown ticket provider might be a challenge for lounge access in HKG, probably inferior to "The Pier", if access at all.

Regarding the LH seating: Far from CX/SQ quality, though, survivable, not that bad, provided you have a window seat. When you sleep on your left side, go for the A side, otherwise the K side.