(a) The District Commander is authorized to modify or waive any requirement prescribed in this part whenever, in his or her judgment, the safety of marine commerce will not be impaired by so doing.

(b) When the District Commander shall determine that changed circumstances in the case of a structure, whose obstruction lights and/or sound signal have been modified or waived, constitutes a hazard to marine navigation, he or she is authorized to revoke or revise his or her previous action and to require the structure to be appropriately marked by suitable obstruction lights and/or sound signals in accordance with this part.