Let's say you chose not to book the tightest connection offered by the airline or couldn't because it was outside the MCT. As it happens your incoming flight arrived early and you now have plenty of time to catch an earlier connection. You've got no checked luggage. Will airlines generally put you on this flight if you ask them?
I know Easyjet will do this for the inbound part of a return ticket and recently something like the above scenario happened to me when connecting in Copenhagen and Cimber Air (a small Danish airline) put me on an earlier connection free of charge. I'm just wondering if the major national carriers like KLM or BA are willing to do the same if you ask them.