How can we make the item code field editable in PO lines converted from RFQs?

In our current process for creating negotiations related to a construction project, buyers often do not have the item code available because the negotiation includes a Bill of Quantities (BOQ). As a result, they create the negotiation without specifying an item code.

After the award is converted to a purchase order, the item code field remains inactive, requiring users to delete all lines and re-enter them, which is time-consuming.

How can we make the item code field updatable in the purchase order lines, allowing users to select the appropriate item code within the PO lines themselves?