RSSP Requisition edit/change order to add lines. PO still in Classic UI

Summary:

Requester Requisition edit to add new lines to an existing linked, approved PO. Is this possible?

Content (please ensure you mask any confidential information):

Requester has submitted a Requisition that has been processed to a PO. Project changes require additional lines to be added to the PO, often of different line types. Existing lines cannot be edited for this purpose. Attempts to add new lines result in limitations to the line types already used.

Requester has also attempted this process by duplicating the Requisition, deleted and added new lines but either cannot submit the Requisition due to errors or, if can be submitted, the Buyer is unsure how to use Requisition Processing to link this Requisition to the existing PO.