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you could configure the save button to save and continue. This will save the form but leaves it open for further editing. You only need to make sure you provided all mandatory information.
In the background a workflow can run when the button is clicked. This workflow could use a create item action to create a new item with the information you want to transfer to it.
Would that be useful in your case?
Using this approach you might think of a second save button that the user can hit to save the item but without starting the duplication too.