Oh... I missed that important part: You were going to change an SJC-OAK one-way rental to SJC-SJC. Then the reverse (in terms of rate) of my statement would hold true, as Tuneman1984 said, the rate should go down, from the high one-way to ordinary.

Even weekday ex-airport rates are usually half of one-way rates, so even if you just turn up at SJC to return it, you will probably get charged the recalculated, i.e. lower, rate. But if you want to make sure, call Hertz, get recalculated quote and if you are happy with the new rate, change the reservation before dropping off at SJC.

In my experiences, while I have not changed drop-off locations, when I turn in the car earlier than what I have reserved, my actual charge was less than my reservation quoted, reflecting the early return. As an example, when I rented out of SEA on a weekend with a 2-day minimum PC for 3-day (Friday 11AM to Sunday 7PM), I decided to check-in early for my flight and returned the car on Sunday 9AM -- I got charged less than quoted by exactly one-day rate since the 2-day minimum conditioon for the PC was still fulfilled.