Subject to the provisions of this Act, every person employed in the library immediately before the date of establishment of the Board shall, on and from such date, become an employee of the Board with such designation as the Board may determine and shall hold his office or service therein by the same tenure, at the same remuneration and upon the same terms and conditions as he would have held the same on such date if the Board had not been established and shall continue to do so unless and until his employment in the Board is duly terminated or until such tenure, remuneration and terms and conditions are duly altered by the Board:
     Provided that the tenure, remuneration and terms and conditions of service of any such person shall not be altered to his disadvantage without the previous approval of the Central Government.