A person may not construct, or cause to be constructed, a facility in the coastal area unless he first obtains a permit pursuant to these regulations. If an application is, in the determination of the Secretary, substantively modified after the review process begins, the application, as modified, shall be processed and evaluated in accordance with these regulations. Facilities for which on-site construction, excluding site preparation, has legally begun before July 1, 1975, are exempt from the provisions of the Coastal Facilities Review Act.