Hi,
Rather then restricting the value for a condition type in PO.
You can enter the desired value in Info-record and default the same in PO and restrict manual changes for those condition in PO.
You can maintain the condition value in condition record based on validity date and default in PO.
If still you want to restrict the value at PO level based on condition type then check the below Badi and method processing.
Badi:ME_PO_PRICING_CUST
Method: PROCESS_KOMP
