A nonconforming building or structure may be altered (but not enlarged or extended) during its life to an extent not exceeding in aggregate ten (10%) percent of the recorded true value, as appraised in the records of the Tax Assessor of the Borough, only upon application to the Board of Adjustment and notice to all property owners, such notice being given in conformance with N.J.S.A. 40:55D-1, et seq.