PO Change Order - Approval of Change Amount vs Full PO Reapproval

Currently when a requistion is submitted the amount on the requisition determines how far up the hierarchy the AME routes it for approval.  For example; a $5 million requisition might go up 6 levels of approval, whereas a $50 requisition would only go up one. However, when a change order is submitted we want the AME to determine the approval hierarchy based upon the amount of the change, not the full PO amount.  So if $50 is requested to be added to an approved $5 million PO we would only want the first level of approver to have to approve,