Goto va21 over view screen first enter different sold to party then goto create with ref to inquiry then system gives with Warning messge with yellow color, just ignore it and click enter,then system will copy the new SP..
Ravin,
Please find the examples when and why we can change the Sold party in the below document.
very good explanation.
Changing the Sold-to Party - Sales (SD-SLS) - SAP Library
thanks,
Srinu.