End dating Business Processes in Service Contract

I am trying to end date a business process in the service contract in order to accommodate the client's desire to change values of coverage days and times and other values in dff's on the service activity billing types associated with the business process.  The client's requirement is that they be allowed to change these things in advance using a future date so that the changes will not be enacted until the date arrives.  I am facing a problem in trying to add a second identical business process in the contract and receive a validation message that prevents adding the second line to the