(a) A trust company shall establish and maintain a common trust fund only in accordance with a fund plan that is approved:
(1) By resolution of the board of directors of the trust company; and
(2) By legal counsel.
(b) Notwithstanding any provision of law that applies to a participating fiduciary account, a fund plan controls:
(1) Participations in the fund; and
(2) The rights and benefits in participating accounts of all persons who have interests in the fund.