I had this happen and was able to switch both the outbound and return of award flights. Was originally on the evening HA SAN-HNL flight and there was a schedule change, agent allowed me to switch to the midday AS flight. For the return I was on HNL-LAS-SAN and another schedule change allowed us to switch to the direct HNL-SAN. Agents in both cases looked at AS and HA flights for the switch.