Unfortunately, I just tried the steps above and it doesn't work for me. This is the error I get every time I am on the last step to reconfirm the modified reservation "CHANGE REQUEST CANNOT BE ACTIONED- MUST CANCEL AND MAKE NEW RES [DE685]"
I believe this could be due to the fact that this was a prepaid reservation .... seriously, didn't expect something so simple would be made so complicated by Hertz