Mo. Rev. Stat. § 456.1090: Power to contract — presently exercisable power of appointment — power of appointment not presently exercisable.

1. A powerholder of a presently exercisable power of appointment may contract:

(1) Not to exercise the power; or

(2) To exercise the power if the contract when made does not confer a benefit on an impermissible appointee.

2. A powerholder of a power of appointment that is not presently exercisable may contract to exercise or not to exercise the power only if the powerholder:

(1) Is also the donor of the power; and

(2) Has reserved the power in a revocable trust.