While a nonconforming use may not be extended, nothing contained herein shall prohibit the extension of a lawful use to any portion of a nonconforming structure which existed prior to the effective date of this chapter. Further, nothing contained herein shall prohibit the replacement of any mobile home legally existing in the Town of Stockport at the time of adoption of this chapter, provided that the replacement structure is in full compliance with the specific standards established in § 120-39B(1) through (4), which compliance shall be reviewed in accordance with the special use permit procedure stated within Article V. No nonconforming use shall, however, be extended to displace a presently conforming use.