How to create a BPM Worklist rule for Requisitions preventing Agreement Line Amount overage?

When submitting a Requisition line, related to a Purchase Agreement (BPA or CPA), we want a check if the amount of the Requisition line exceeds the AMOUNT_LIMIT minus AMOUNT_RELEASED of the related Purchase Agreement. And if possible, if the sum of the amounts of all Requisition lines (of this Requisition), related to the same Purchase Agreement exceeds the AMOUNT_LIMIT minus AMOUNT_RELEASED of the related Purchase Agreement.

We use BPM Worklist for approval of Requisitions.
Questions for this issue, where (sum of) Requisition (line) amount(s) is greater than AMOUNT_LIMIT-AMOUNT_RELEASED:

1. Is it possible to create a BPM rule where the Requisition can still be approved, but the Purchase order is not generate automatically (although Generate orders is set to Yes at the Purchase Agreement)?