Employees of the department shall serve in the unclassified service of the state merit system as defined by Code Section 45-20-6, provided that employees who serve in the classified service of the state merit system as defined by Code Section 45-20-6 may elect to remain in the classified service and be governed by the provisions thereof; provided, however, that if such person accepts a promotion or transfer to another position, he or she shall become an employee in the unclassified service.