I have had no trouble changing my destination in the event of weather (I have done this several times on several airlines between LAX, SNA, ONT and SAN). I have also changed the origin to another nearby airport that was driveable with no problems. The key would be that your actual flight would need to be affected (i.e. I have never gotten a "proactive" change and have always had to wait for my actual flight to be cancelled/delayed - even when all signs pointed to it happening but the event had not occurred yet).