From the Commentary to Regulation DD:
Institutions need not disclose reservations of right to require notices for withdrawals from accounts required by federal or state law.
If you did not disclose the restriction, the change is in the customer's favor and there's no real argument that you need to disclose the fact that it has been eliminated.
Focusing only on the conversion of interest bearing NOW's to interest bearing DDAs, in general the call report issues you mention are paramount. Review your NOW account disclosures line by line to make certain that's the case in your institution. Ironically, if you have gratuitously referred to the account as a "NOW" account, you might want to tell the customer what the new name is, but heaven help you if you attempt to explain why.
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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.