how the users should be able to modify prices for partial-shipped lines

The users should be able to modify prices for non-shipped lines, even after some lines from the order have been shipped.

For Example customer orders 200 pieces of product A in January and we ship 100 of them in May. Now, the customer wants the remaining 100 pieces to be shipped in June. But, price of the product A got reduced due to market competition. So, CPQ does not allow to change the prices for those partially non-shipped 100 pieces.