Loans made under this subchapter shall be payable in not to exceed seven years. The Secretary may consolidate or reschedule outstanding loans for payment over a period not to exceed seven years (or, in the case of loans for farm operating purposes, fifteen years) from the date of such consolidation or rescheduling, and the amount of unpaid principal and interest of the prior loans so consolidated or rescheduled shall not create a new charge against any loan levels authorized by law. A new loan may be included in a consolidation. Such new loan shall be charged against any loan level authorized by law. Except as otherwise provided for farm loans under section
1981b of this title, the interest rate on such consolidated or rescheduled loans, other than guaranteed loans, may be changed by the Secretary to a rate not to exceed the rate being charged for loans made under this subchapter at the time of the consolidation or rescheduling. The interest rate on any guaranteed loan under this subchapter that may be consolidated or rescheduled for payment shall be such rate as may be agreed upon by the borrower and the lender, but not in excess of a rate as may be determined by the Secretary.