BPM Rule to reject Change Order if Cost Center is changed

Hi,

Is there a way to auto reject Change Order if Cost Center is changed. But at the same time if we add a new requisition line to existing PO it should not auto reject.

I tried using PurchasingDocumentDistribution.chargeAccountModified is "Y" but it's auto reject the Change Order if we add a new requisition line to PO.

Any suggestions ?

Thanks