Originally Posted by AutoSlash

Chances are basically nil. Any change is going to cause a re-rate of the whole rental. The good news is that you can just return one day late and be charged the proportional rate for an extra day without impacting your original rate plan. Give them a call (or use the mobile app depending on company) to extend your rental. You can skip this step and just return late but they may charge you an extra $25 or so as a late penalty on top of the 1-day rate.

Hope this helps. Safe travels!

Originally Posted by mia

We extended a Hertz rental at Christmas: https://www.hertz.com/rentacar/misc/..._extension.jsp