A promise by a creditor which for any cause is void or voidable by him at his option does not alter the obligation or suspend or impair the remedy within the meaning of § 56-1-22 . Source: SDC 1939, § 26.0117.
Void promises do not exonerate guarantor
SDCL § 56-1-23, under GUARANTY.
SDCL § 56-1-23