This is a change that has been contracted for and the borrower agreed to the change in writing when signing the contract. I really don't believe a notice would be required, however for open end plans I would err on the side of caution and supply the notice.
As a side note, we don't take advantage of the ability to change the late charge when the state increases the allowable maximum, so I have not spent time researching the notice requirements, if any.
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The opinions expressed are mine and they are not to be taken as legal advice.