OAK, SFO, and SJC are all co-terminal cities so yes, if you are eligible for reaccom you can go to either of the cities. Reaccom is available, for a one time change (unless your new flight delays as well) for any delay over 15 mins at the airport or 60 minutes if you call into res. For a trip already in progress, the airport must do it since the funds for the flight are already pulled and Res has to go through multiple hoops to get it changed.