Minor changes to these existing uses shall be permitted, including additions to or changes to existing buildings or construction of new accessory buildings, subject to applicable standards; provided, however, that any such changes of the existing uses shall only be permitted if there results no intensification of the existing use of the property as of the date of adoption of this article creating the district. For purposes of administering this requirement, an intensification of use shall be construed to mean any change in site activity which would have a significant negative impact upon residential properties in the vicinity, including but not limited to increased vehicular traffic, outdoor storage, an increase in nighttime operations, increased noise, odors and other emissions, etc.