How to create substitute items against an item for Manufacturing without item structure

Summary:

We are using Process manufacturing where we need to define substitute items against many raw materials which can be add/view/manage in Work definition, Work order creation and Work Order Execution. I have seen that it can be achieve through creating item structure after 23A. But need to know is there any way to define without item structure and whenever user using the items it will show the respective substitute items.

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Version (include the version you are using, if applicable):

23C

Code Snippet (add any code snippets that support your topic, if applicable):