I too discourage this. While the chances that you'll be black-listed from the airline in the future are slim, there is a good chance that the onward portions of your journey will be cancelled.

I'm currently on a oneworld RTW. My last segment is an AA 767 flight EZE-JFK. Since the thought of such a long flight on a 767 is a negative one, I'm considering rebooking on UA for that flight. It's the last segment, so there aren't any onward segments that could be cancelled.

Again, highly discouraged.