how to update old employee details with new project and cost center?

Hi friends, I need to update a old employee whose services are already ended in year 2005 (version 11.5.10.2). Now we need to update the same employee by assigning him to different project, region and cost center. When I am trying to update, system is not allowing me to change the department (cost center) because this employee is already assigned to different (organisation) department before. So, can anybody help me in this issue, please? Thanks, Prakash