Mo. Rev. Stat. § 456.1135: Application to existing relationships.

1. Except as otherwise provided in sections 456.970 to 456.1135:

(1) Sections 456.970 to 456.1135 shall apply to a power of appointment created before, on, or after August 28, 2016, and shall apply to a judicial proceeding concerning a power of appointment commenced on or after August 28, 2016;

(2) Sections 456.970 to 456.1135 shall apply to a judicial proceeding concerning a power of appointment commenced before August 28, 2016, unless the court finds that application of a particular provision of such sections would interfere substantially with the effective conduct of the judicial proceeding or prejudice a right of a party, in which case the particular provision of such sections does not apply and the superseded law applies;

(3) A rule of construction or presumption provided in sections 456.970 to 456.1135 applies to an instrument executed before August 28, 2016, unless there is a clear indication of a contrary intent in the terms of the instrument; and

(4) Except as otherwise provided in subdivisions (1) to (3) of this subsection, an action done before August 28, 2016, is not affected by such sections.

2. If a right is acquired, extinguished, or barred on the expiration of a prescribed period that commenced under law of this state other than sections 456.970 to 456.1135 before August 28, 2016, the law continues to apply to the right.