How to allocate less than ordered qty

Summary: Is there any way to allocate less than the ordered ordered quantity even if there is enough inventory to fulfill the entire amount?

For example we have 2,000 in inventory of Item A, order calls for 1,000 but we only want 500 allocated and the other 500 cancelled.

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Version (include the version you are using, if applicable): 22C

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