SDCL § 55-18-23: Provisions of governing instrument.

A governing instrument may require additional notification or consent than otherwise required by law. Unless expressly authorized by the governing instrument, a person designated by a governing instrument to represent another person or class of persons may not represent such person or class of persons while that designee is serving as a trustee or co-trustee of such trust.

A governing instrument which authorizes a person or fiduciary to appoint a representative may also identify or describe a person, several persons, a class of persons, or a description of persons who may not be appointed as representatives as to all or certain represented persons or matters or during a period of time.