If the check is returned NSF and we choose to clear for a second time and not charge back to the customer we would then need to send a second "reasonable cause" notice to the customer to extend the hold for 7 days from date of redeposit. Is my thinking correct?
That's a different question altogether; John's response did not bless that. In candor, it should be the customer's decision to reclear a check, not the bank's. You assume significant risks when you automatically reclear an item without the customer's knowledge or permission.
Back to the first question, you do not backdate the hold notice. You simply use the original banking day of deposit to calculate your hold period.