A nonconforming use or structure may be continued but shall not be enlarged or extended. In the event a nonresidential nonconforming use or structure is partially damaged to an extent less than 50% of the equalized assessed value of the damaged structure, it may be rebuilt to the extent which previously existed within one year from the date of damage. In the event such a use or building is damaged to an extent greater than 50% it may only be rebuilt upon approval of a use variance or such other variance as is provided by the Municipal Land Use Act 40:55D-1 et seq. In the case of nonconforming radio transmitters, these uses may be rebuilt if changes in technology produce a more advanced type of transmitter provided site plan approval first be obtained from the planning board.