The role can be changed from Past Candidate to Past Student by re-enrolling them into the school and withdrawing them.

To do this:
  1. Navigate to CORE > Users > Edit User Profile Data
  2. Search for the student 
  3. Select their name
  4. Scroll down to System Information and select Student Enrollment
  5. Copy the School year, grade, and depart date of the last year the student was at the school
  6. Click Re-enroll
  7. Keep the default settings and click Save and Exit
  8. Click Withdraw
  9. Mark Effective Immediately
  10. Select the student's last school year attended 
  11. Enter the depart date
  12. Mark role: Past Student
  13. Click Save and Exit 
  14. Click Confirm