Whether or not you charge a fee is immeterial. You are modifying the terms of the loan and your loan agreement probably requires a written agreement of the modification.
Would I include the amount of the fee in the modification agreement? Of course! Let's not get into a "he said", "she said" arguement down the road. Not disclosing could be considered deceptive.
Is this a Reg. Z Disclosable Event? No, a subsequent event- but Reg. Z does not require disclosure.
Al
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Al Miller, CRCM
Opinions expressed are my own and not necessarily shared by my employer.