Once a nonconforming use or structure has been changed to conform,
it shall not revert back to a nonconforming use or structure. Once
the Zoning Board of Appeals has permitted the substitution of a more
restrictive nonconforming use for an existing nonconforming use, the
substituted use shall lose its status as a legal nonconforming use
and become subject to all the conditions required by the Zoning Board
of Appeals.