A Board may, with the previous sanction of the Central Government, apply any sums, out of moneys which may come into its hands under the provisions of this Act and which can be so applied without prejudicing the security of the other holders of Port Trust securities, in repaying to the Government any sum which may remain due to it in respect of the principal of any loan although the time fixed for the repayment of the same may not have arrived:
     Provided that no such repayment shall be made of any sum less than ten thousand rupees; and that, if such repayment is made, the amount of interest in each succeeding instalment shall be so adjusted as to represent exactly the interest due on the outstanding principal.