S.D. Codified Laws § 58-6-27
A domestic or foreign insurer holding a valid certificate of authority to transact insurance in this state immediately prior to July 1, 1966, may continue to transact the same kinds of insurance as permitted by such certificate of authority by maintaining thereafter unimpaired not less than the same amount of paid-in capital stock, if a stock insurer, or not less than the same amount of surplus, if a mutual or reciprocal insurer, as required under the laws of this state for such authority in force immediately prior to July 1, 1966, and as if such laws had continued in force. Once a stock company has accumulated the capital and surplus to exceed the minimum capital and surplus for the line authorized pursuant to § 58-6-23, then § 58-6-23 shall apply. Once a mutual company has accumulated the capital and surplus to exceed the minimum capital and surplus for the line authorized pursuant to § 58-5-21, then § 58-5-21 shall apply.
SDCL 58-6-27