Mutes are feral, though I think are protected under the MBTA and I THINK are fair game in PA since the PGC is invovled in a mute swan management plan and they have indicated a poplulation goal of 0 wild mutes.
Feral mute swans are not protected and may be shot. However, be careful that they are feral and are not owned by someone because you could be held liable for killing them as not all Mutes are feral. Generally, feral swans can fly while those owned by someone are pinioned and cannot fly. This is for PA, some states do protect them.