You can list that you have received special training in rehab; having recieved a certificate. Any training that you received as an LPN can be used on your resume, just list it under "Education" or "Continuing Education". I wouldn't put "certified", as that is implying that you had taken and passed the Association of Rehab Nurses course and test to be a Certified Rehab Registered Nurse, and I'm not sure that would have been the case, having been an LPN when you were "certified". I would contact the ARN and check with them. Good luck with job search!!!