Substituable Materials in Production Orders

Hello SAP Experts,

I have a client that needs to change materials in a production order (copied from the BOM) because materials can vary within each order, however versions and material configuration is not applicable in this case. What they want is to be able to include, exclude or change a material in the production order which I know is duable in standard SAP, however when they change a material for another they want to able to select within a range of possible materials, in other words they want to restrict the materials for which a specific material can be changed in a production order.

Regards,

Patricia