In case anyone is curious regarding how this worked out, they charged me a $50 one-way fee.

When I picked the car up at ITO, I asked to change the drop-off location and they refused. The day I was due to drop the car off, I called the national office and they said they couldn't help because the change wasn't a drop-off to another airport location, and transferred me to the ITO local office. This time the ITO office modified the reservation, but wouldn't agree to amend the drop-off fee despite not charging it on any other vehicle type.