I can imagine it's easier to move you to CX if you are going to HKG. It's cheaper for them to pay CX rather than get you a night plus food and drinks plus the EU compensation at FRA.

Personally I prefer MUC than FRA because almost all the time I connect there it involves a long walk (through a long tunnel). I also had to wait in a bus to the aircraft for 30 mins for a flight to DFW - then everyone had to walk out of the bus to the staircase to get on board. Before we sat down on board the plane started moving.

Not sure how flexible it is for them to move anyone to an SK metal but I don't really care because IMO flying with SK on Y is like flying with a low cost airline. Also I don't think I'll be willing to do so because it might affect the mileage accural (for M&M there will be no mileage given for flights not operated by LH).