Lock prior created receipt amounts when changing price on a Purchase Order

Summary:

When updating a price/rate on a partially receipted/invoiced PO (as per Doc ID 2671541.1) is there a way to stop the existing receipts from utilising the new rate/price.

Content (required):

Our Business Users have a requirement to update the price on rate based service PO's every 3-6 months due to Government mandated rate increases.

We cannot create a new line on the Purchase Order as our Business Users can only view invoice/receipt details via the Requisition Lifecycle page and if we add a new line the users lose oversight of this new line (as the new line is not linked to the original requisition).