Making changes to a PR after it has been Submitted for Approval

If User A creates a Purchase Requisition, submits it for Approval, can User B change it?

Purchasing would like the ability to change Purchase Requisitions in flight.  An example of this is, User A orders 3 iPhones for $500 from Verison and submits it for Approval; Purchasing reviews the PR and determines that User A should have ordered 3 Samsung Phones from ATT and changes the PR.  The PR is not cancelled or rejected, after Purchasing has made their changes, the PR is allowed to continue in the Approval process to the next Approver.  User A will not be involved the change process and will see the changes on the PO has been created from the