Originally Posted by SK AAR

Once the OP has been rebooked, LX is not going to rebook again just because a more favorable connection has become available. The OP should have waited to request a rebooking until Y seats became available for BRU-MUC. I second that most likely Y seats will become available closer to departure date so the OP should have waited (yes I know that such wait is nerve wracking)

It is extremely unlikely that that OP would have been rebooked into J/C class when ticketed in Y even if more seats had been available.

Return flight: Unless the OP was already rebooked for 2 days later by the phone agent, LX ticketing department is certainly not going to do the rebooking. Asking to postpone the departure date by 2 days when the return flights are not cancelled is pushing it IMO and unlikely to be approved. My prediction is that LX ticketing department will do nothing about the return date/flights already ticketed.