Any loan insured pursuant to this subsection shall (A) bear interest at such rate as may be agreed upon by the mortgagor and mortgagee; (B) be secured in such manner as the Secretary shall require; (C) be limited to a term not exceeding the unexpired term of the original mortgage; and (D) be insured under the same section as the original mortgage. The Secretary may provide insurance pursuant to paragraph (2) or (3), or pursuant to both such paragraphs, in connection with an existing project mortgage, except that the Secretary may not provide insurance pursuant to both such paragraphs in connection with the same period of months referred to in paragraphs (2)(B) and (3)(B). The Secretary is authorized to collect a premium charge for insurance of loans pursuant to this subsection in an amount computed at the same premium rate as is applicable to the original mortgage. This premium shall be payable in cash or in debentures of the insurance fund under which the loan is insured at par plus accrued interest. In the event of a failure of the borrower to make any payment due under such loan or under the original mortgage, both the loan and original mortgage shall be considered in default, and if such default continues for a period of thirty days, the lender shall be entitled to insurance benefits, computed in the same manner as for the original mortgage, except that in determining the interest rate under section 1715 o of this title for the debentures representing the portion of the claim applicable to the loan, the date of the commitment to insure the loan and the insurance date of the loan shall be taken into consideration rather than the commitment or insurance date for the original mortgage.