Would like to add one more day to a 10 car rental for early May. Rates have gone up since I booked. Has anyone had any luck getting Chase/Expedia to make an adjustment to the dates on a car rental using the original daily rate?

[EDIT: The UR website says: ...you must cancel your existing reservation and rebook a new itinerary with the changes you need.] So just ignore this question unless you have been able to make an adjustment w/o cancelling.

Looks like I'll just book a 1 day rental for abt 4200 UR.