Hello Naveen,
You're right, these FMs are unreleased FMs that intent to change orders in liveCache directly. You must be very familiar with input information to use them. They're not supported by SAP to be used in customizing program.
You can try BAPI_POSRVAPS_GETLIST3 and BAPI_POSRVAPS_SAVEMULTI3.
Best Regards,
Ada