Sec. 4. (a) The department may do the following regarding purchasing and contracting by state agencies:
(1) Adopt rules under IC 4-22-2 necessary to implement IC 5-22.
(2) Consider and decide matters of policy.
(3) Enforce IC 5-22 and rules adopted under subdivision (1).
(b) The department may not adopt rules that affect the rights or obligations of the state or of a contractor under a contract in existence on the effective date of a rule.