Yes. Unless the Trading Partner is doing something that does not follow HL7 convention, you can handle such customization by modifying the HL7 message schema to accomodate the differences.
In this case, just add two additional child elements to the PV1 to accept the new data.
You will also have to change the TargetNamespace of the modified schema to isolate it to this Trading partner and set that on...one of the tabs (sorry don't recall exactly) in HL7 Configuration.