Update Pay Terms on PO after Supplier Pay Terms Change

We have recently implemented ACH payments, so we have been updating the pay terms on our suppliers from N30 to NOW. When creating a voucher in regular entry, we "Copy from Purchase Order Only" to select PO lines for the voucher. When we do this, the supplier pay terms update from the supplier defaults (NOW) to the defaults when the PO was created (N30).

Is there a way to update the supplier pay terms on an existing PO? If not, what is a recommended course of action?