The only time that disclosure is not required is if changes are being made to "protect the security of a funds transfer system." Changing vendors does not fall into this category so 21 days advance notice would be required since we are reducing the type of available funds transfers. These is no carve out for a short period of time.
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Sola Gratia, Sola Fides, Sola Scriptura, Solus Christus, Soli Deo Gloria!
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