The provisions of section thirty-five B shall not be construed to prohibit the maintenance, repair or replacement nor to require any change in the height or location of any structure existing prior to the initial approval of an airport by the commission or prior to the construction of a runway or landing strip at an airport so approved.
Notwithstanding the provisions of section thirty-five B, an addition in height or otherwise may be made to any structure which exceeded a height of one hundred and twenty-five feet above ground prior to the initial approval, after January first, nineteen hundred and sixty, of an airport by the commission or prior to the construction of a runway or landing strip at an airport so approved after said date.
For the purposes of this section initial approval shall be construed to include reapproval where approval has been withdrawn for a period following initial approval.