Actually, the only change in your procedures is that you would not charge them a fee if they overdrew their account via a one time debit card or ATM transaction. Their opt-in was an illusion.
While I don't believe there is any requirement for a notice, if you want to send something indicating the opt-in is no longer available I suggest you send it to everyone who was solicited for an opt-in, not just those that did.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.