Often I book a return ticket with a transit, and then ditch only the route from the transit to the destination of the return flight. In other words, I get off at the transit place only in the return flight.
However, I have an experience of being handed a direct ticket in case of an emergency, even though the original ticket included a transit. For example, my original ticket was from Seoul to Tokyo with Shanghai as a transit, but since the flight operated by China Eastern was delayed for some reasons, I was instructed to get on a flight operated by Korean Air to directly go to Tokyo.
At that time, I didn't plan to get off at Shanghai, so it was not a problem. However, now I wonder if it is possible to decline the alternative ticket handed at the check-in counter. I usually book an onward ticket as well as my room in advance before stating that I like to get off at the transit airport; even the airline staff told me that I must state it at the check-in counter since they don't accept it via a phone call or email in advance.
So can I decline the alternative ticket? If not, is it the airline or I that should book another ticket that can get me off at the transit airport?