How to override TAXABLE_FLAG on existing Approved Purchase Orders?

Summary:

Business wants to update the Taxable Flag to N on Purchase Order Documents, as the POs were initially created with Taxable Flag as Yes. Please advise is there any way to override Taxable Flag on Purchase Orders.

Content (required):

It seems Taxable flag was derived from Item Master. If we update Taxable flag at Item Master then all the new POs are reflecting with N, however we want to update Taxable Flag on existing POs, as the POs are with huge Dollar amount and we can't cancel those POs.

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

23B (11.13.23.04.0)