To put another way, if the ACH item is for account #12345, and #12345 is NSF, your choices are 1) return as NSF, or 2) pay into further OD. Transferring to another account the customer owns is not an option via either NACHA Operating Rules or Reg E.
And if the customer disputes, you can't deny - you have no legal basis for doing so.
Now, I would guess that someone in your back office may think this is "a great customer service they are providing" by ensuring that a recurring item is not returned, But you have no legal basis for doing this, so you should be aware of the risks associated and really should make sure it discontinues if this is a normal practice.
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