Following the adoption of the classification plan and the allocation of classes therein, the class titles set forth therein shall be used to designate such positions in all official records, vouchers, payrolls, and communications. No person shall be appointed to, or employed in, a position in divisions of the service subject to this chapter pursuant to subsection 1 of section 36.030 or a position in a department or agency of state government subject to this section pursuant to section 36.031 under a class title which has not been approved by the director as appropriate to the duties to be performed.