Originally Posted by
GoSh4rks
Assuming UA metal, It can be done as a change, not a cancel and rebook. At least the 1k agents can do it this way, even without x/xn availability (if that's what was originally booked.)
Based on the stated connection time I'm pretty sure we're talking an all UA itinerary. It could be done even if NRT were on NH, but that is a little dicier.
I concur with sinoflyer that OP should consider changing to an earlier UA flight. The Capitol Express from Sacramento is not a great option if your destination is SFO.