Sorry, I know people here don't like these questions and feel they have been asked a million times, but I am looking for recent experiences.

I have an inbound ORD-LHR-ZRH. It's booked on AA, but both flights are on BA metal. Now my plans have changed and I need to be in Berlin instead of Zurich. My question is: if, hypothetically, I would travel with hand luggage only and would drop the last leg, would it be still possible to board another plane LHR-TXL on a BA ticket? (e.g. booked with Avios)? Or would the staff at the gate say, 'Hey, you're supposed to be on that other flight'? Has anyone tried that?

I could, of course, chose another carrier, but that would mean changing terminals etc. BA would be just more convenient...