AX 2012 Workflow approval upon PO changes

Please suggest a standard ax way out where PO needs a change having workflows.

For example - PO worth £2000 approved and changed to £1500, no re-approval asked( good). However, if the same change would have been over the amount of originally approved PO (from £2000) to £2500, standard AX enforces re-approval of the same (not good from the business's requirements point of view). Please advise if any way to set tolerances bypassing re-approval on a certain amount. Say if bandwidth of 10% above or below approved PO would be acceptable and need not to go through a re-approval process.

Advice awaited