Quantity and price change on a purchase order in receipt routing

We are using Receipt Routing to track inventory while the inventory on its way from supplier to receiving facilities.

The process is to create a PO, Receive it when supplier ships and enter receipt routing steps till the last step ie move to stock. Payment can be made either at the time of Receipt or at the last movement i.e. move to stock . The whole process is a mutli day process.
Due to nature of business, the price and exact quantity thats on shipment to client can change while its enroute.
1. How can we update quantity and PO price while its in receipt routing.