Any variance, made without the suretys consent, in the terms of the contract between the principal [debtor] and the creditor, discharges the surety as to transactions subsequent to the variance.
Illustrations
(a) A becomes surety to C for B's conduct as a manager in C's bank. Afterwards, B and C contract, without A's consent, that B's salary shall be raised, and that he shall become liable for one-fourth of the losses on overdrafts. B allows a customer to overdraw, and the bank loses a sum of money. A is discharged from his suretyship by the variance made without his consent, and is not liable to make good this loss.
(b) A guarantees C against the misconduct of B in an office to which B is appointed by C, and of which the duties are defined by an Act of the Legislature. By a subsequent Act, the nature of the office is materially altered. Afterwards, B misconducts himself. A is discharged by the change from future liability under his guarantee, though the misconduct of B is in respect of a duty not affected by the later Act.
(c) C agrees to appoint B as his clerk to sell goods at a yearly salary, upon A's becoming surety to C for B's duly accounting for moneys received by him as such clerk. Afterwards, without As knowledge or consent, C and B agree that B should be paid by a commission on the goods sold by him and not by a fixed salary. A is not liable for subsequent misconduct of B.
(d) A gives to C a continuing guarantee to the extent of 3,000 rupees for any oil supplied by C to B on credit. Afterwards B becomes embarrassed, and, without the knowledge of A, B and C contract that C shall continue to supply B with oil for ready money, and that the payments shall be applied to the then, existing debts between B and C. A is not liable on his guarantee for any goods supplied after: this new arrangement.
(e) C contracts to lend B 5,000 rupees on the 1st March. A guarantees repayment. C pays the 5,000 rupees to B on the 1st January. A is discharged from his liability, as the contract has been varied, inasmuch as C might sue B for the money before the 1st of March.