Section 217.209 - Modifications of Letters of Authorization(a) Except as provided in paragraph (b) of this section, no substantive modification (including withdrawal or suspension) to the Letter of Authorization by NMFS, issued pursuant to § 216.106 of this chapter and § 217.207 and subject to the provisions of this subpart, shall be made until after notification and an opportunity for public comment has been provided. For purposes of this paragraph, a renewal of a Letter of Authorization under § 217.208 , without modification (except for the period of validity), is not considered a substantive modification.(b) If the Assistant Administrator determines that an emergency exists that poses a significant risk to the well-being of the species or stocks of marine mammals specified in § 217.202(b) , a Letter of Authorization issued pursuant to § 216.106 of this chapter and § 217.207 may be substantively modified without prior notification and an opportunity for public comment. Notification will be published in the FEDERAL REGISTER within 30 days subsequent to the action.