Capex Overspend Budget limit

Hi

Can anyone tell me whereabouts you change the "overspend" threshold for purchase orders on capital projects, and whether or not it's possible to extend the criteria to include manual postings via Accounts Payable and manual expenditures on the project themselves.

We have had occasions where projects have gone over budget because of additional AP postings which haven't been included in the 10% overspend limit we currently employ.

Thanks

Martin