Data point:
Last night departing JNB in Business on DL 006 award…original route JNB-CDG-AMS-OSL (all AF flight numbers).

AMS-OSL cancelled. Staff in JNB took control of 006 ticket and protected on SK CDG-OSL in C class (AF flight was overbooked). Reissued to 057 ticket.

Was fairly straightforward.

Only issue was transfer to T1 in CDG.