There is no dedicated function to rename a system database. You can however folow the procedure described under. 

  1. Open the System Database Window.
  2.  Select the system database to be renamed in the System Database list.
  3.  Click the “Copy” button and give the new (reanamed) name.
  4.  Test that the copied WBS works.
  5.  Go back to the System Database Window. Select the system database that you now have saved with a new name, and click the delete button to delete it (or alternatively, uncheck the “Active” checkbox to keep it but not having it show up in the selections in the Login window).