A contract not in writing may be altered in any respect by consent of the parties, in writing, without a new consideration, and is extinguished thereby to the extent of the alteration.

Source: CivC 1877, § 968; CL 1887, § 3592; RCivC 1903, § 1286; RC 1919, § 907; SDC 1939, § 10.0805.