PO Release stratergy to trigger for only PO Extensions or only on New PO Line Item addition

Hi Gurus,

We have a requirement that while the PO is created after approval from HR system ( E-rec System),  there was no need of PO Approval and Release strategy in SAP POs getting uploaded... so there is right now no release strategy nor Release Process in already created existing POs in ECC,

Now we need to extend the already created POs ( and this process and approval process for the same cannot happen in HR, E-Rec system )..

so now the Requirement is, can we have PO Release strategy to trigger or get activated when we do PO Extensions (adding new line item to existing PO)

FYI... there is no release strategy at the PO Header as of Now..

please suggest ideal Approach to achieve the same..

Thanks and Regards

Sari