How can I change the requisition line source after the requisition is approved?

Summary:

How can I change the requisition line source after the requisition is approved? When creating the requisition, the source is defaulting to BPA or Inventory. However, if the buyer wants to change the source from BPA to Inventory, or vice versa, the system is not allowing the update. Is there any way to do this? Is this a standard functionality?

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):