Change Price in PO refer to contract

Hi gurus,

I need to be sure that price in a PO which refers to a contract, is 100% identical from price into the contract.

In standard, PO net price field linked to an agreement can not be changed, which is fine with my requirement.

Nevertheless, if you change PO document type such as AC to one which does not refer to a contract such as NB, and then change the price, you can go back to the initial PO document type AC which refers to the contract and save! In that case, PO price differ from contract price; which is what I absolutely want to avoid.

Is there a way that SAP can make a check of these 2 prices and send a message around the difference before saving the PO? Or another way to avoid this situation?

Thanks