36 CFR § 9.150 - How can an approved permit be modified?
(b) The Regional Director may propose to modify an approved temporary access or operations permit to address changed or unanticipated conditions within your area of operations. You will be notified in writing of the proposed modifications and the justifications therefore, and the time within which you must either notify the Regional Director that you accept the modifications to your permit or explain any concerns you may have
(c) The Regional Director will review requests made under paragraph (a) of this section or responses provided under paragraph (b) of this section applying the approval standards and timeframes at § 9.62 or § 9.104, respectively. You will be notified in writing of the Regional Director's decision and any revisions approved to the terms of the permit.