If you have enough miles, and want to make another trip to Japan within a certain period, you may change existing NRT-SJC to some date, then book another award such as
NRT-SJC//SJC(or any N.A airport)-NRT(or any JP airport)
or RTW award (or any award which starts from NRT-SJC, then return to Japan)
NRT-SJC-RTW-JPN