The otherwise lawful use of any structure or land existing as of May 27, 1976, may be continued. However, a modification of an existing use or development is subject to the provisions of COMAR 08.15.02 unless the modification is exempted under COMAR 08.15.02.02. If a non-permitted use or development is discontinued for 1 year, it may not be reestablished thereafter and any future use or development shall be in accordance with these regulations.