May the lateral boundary (the legally established river corridor) of a wild and scenic river be amended?

Yes. The Wild & Scenic Rivers Act anticipates the need for occasional adjustment of the lateral (river corridor) boundary, directing that such amendment follow the same process as described for the initial boundary development in Sections 3(b) and (c) of the Wild & Scenic Rivers Act. The legally established river corridor might require amendment to better reflect protection of outstandingly remarkable values or as the result of identification of a new outstandingly remarkable value.