Mo. Rev. Stat. § 288.370: Law does not confer vested rights.

The legislature reserves the right to amend or repeal all or any part of this law at any time; and there shall be no vested private right of any kind against such amendment or repeal. All the rights, privileges, or immunities conferred by this law or by acts done pursuant thereto shall exist subject to the power of the legislature to amend or repeal this law at any time.