The board may establish a designated Roth contribution program within the deferred compensation plan. For purposes of this section, a "designated Roth contribution" means an elective salary deferral that is:
(1) Designated irrevocably by the participant at the time of the deferred election as a designated Roth contribution that is being made in lieu of all or a portion of the pre-tax elective deferrals the participant is otherwise eligible to make under the plan; and
(2) Treated by the employer as includable in the participant's income at the time the participant would have received that amount in compensation if the participant had not made a deferred election.
The board may promulgate rules, pursuant to chapter 1-26, relating to distributions, conversions, transfers, rollovers, and limitations with regard to the designated Roth contribution program in accordance with federal law.