For purchase orders, we want to have better control over editing an approved purchase order so we have locked them after approval. But there are some necessary changes that do often need to be done on a PO both in the body and line item. I cannot see any way to have a PO require approval and then have any changes require approval. Is this possible or is there a po change order process that I cannot find?

It is a common NetSuite issue, but its solvable. It does require a bit of custom workflow/script magic. The PO would need to remain unlocked; if a field is changed that you deem necessitates re-queueing for approval, you would just tell your PO workflow to requeue for approval

Thanks @Anthony (NimbusLabs)