If the board shall find, by a two-thirds vote of its entire membership, that some project, other than any project (whether original, modified, substituted, or other) already adopted, should be adopted then the board shall proceed under Chapter 1 (commencing with Section 42200) of this part to prepare an additional report which shall be complete in itself and shall set up the project as an additional project for the district. The additional report shall not modify, rescind, or terminate any other project which has already been adopted.