If an employee transfers from a certificated position to a classified one, or vice-versa, the best practice is to use separate Job Data records, as well as separate positions.  Do not do this kind of transfer on either the same position record or the same Job Data record.  The reasons for this range from payroll considerations to retirement reporting issues.  For more information, please refer to the guide "PeopleSoft Human Resources (HR2): Position Management."  Here is a link to the guide: PeopleSoft Human Resources (HR2): Position Management