As per My Understanding Please Follow the below process:
Create a Condition type in Pricing procedure with statistical.
Create the condition table against the condition type as Key combination according to the ship to location.(As per the requirement)
Maintain the condition record on the basis of key combination & maintain the Payment terms as well in the condition record.
when ever you create a sales order depending on the Key combination maintained the Condition record payment terms will overwrite the customer payment terms in sales order .
By doing the above you have restricted the payment terms in Master Level.
Regards
Damu