Add charges on an Approved Purchase Order

Hi,

I would like to setup a PO workflow where when the PO has been approved , I want the ability to resubmit the PO based on the following situations:

  1. the dollar value of the line item on the PO is plus or minus +/- 1% of tha particular line items value. If it exceeds this, then it will need to be resubmitted.

  2. I want to add new line items under the approved PO for freight, shipping/handling & tax without having to go through the workflow again?

Any idea?? Thanks