I would like to control where MRP schedules a Shop Order based on the Machine No field in the Routings. Is there a way to make Machine No. more than just a preference?

For example, I have 1 work center (work center AB) with 2 resources (Resource A and Resource . In the routing for part number 1234, I put resource A in the Machine No field because part number 1234 can only run on resource A, not resource B.

MRP uses Machine No as a preference and if Resource A is at capacity, it will create a Shop Order Requisition for part number 1234 to run on resource B. Is there a way to make MRP schedule resources to run only what's specified in the Machine No field if a resource is entered in?