Hi Murali,
You wan to say change in Account Assignment (WBS Element) in sale Order line item. In this case you have to grant access to Va02 to that particular user and need to guide how to change WBS Element.
Reg., Only access to change Account Assignment for this you need to check with your Basis/Security person. He need to restrict other object for that your.
Or with the Help of ABAPer simple you can create one tool using Sale Order change FM, here you can pass Sale Order, line item and new WBS element which need to be Over right. and you can give this transaction access to the Delivery person.
Reg,
Anand