Data point: LAX-AMS-LIS; November; award ticket; business class; 2 pax. Last week they switched my flights LAX-AMS-LIS from a 3-4 hour layover in AMS to 12-13 hour due to a cancellation of my AMS-LIS segment. I called and was told I had to call Flying Blue. Called and got disconnected. Called and had a magical agent who found me flights on Air France LAX-CDG-LIS. I proposed different flights and he said "sure". On hold for like 60 seconds and got an email confirming the change. No issue flipping carrier.

Today they cancelled my OPO-AMS leg of the return and put me on one that appears to be the following day. However my AMS-LAX leg is still showing the original flights. So I seem to have a negative 20 hour layover.