Grid users re-registering with a new certificate
  Goal
  When a Grid user requests a new certificate there is no need to re-register 
    with a VO, as long as the user's distinguished name has not changed.
  For routine certificate renewals, when the distinguished name is not changed, 
    it is not necessary to register in the VO again. If it has changed then it is 
    necessary to rejoin the VO.
  Resolution
  To retrieve your certificate DN:
  
    - Open the My User Certificates web page.
 
    - Select the appropriate certificate from the list and click "details".
 
    - The Distinguished Name of your certificate is displayed in the certificate
      properties on the right.
 
  
  If needed, follow the VO registration process described at this URL:
    https://twiki.cern.ch/twiki/bin/view/LCG/VomsUsers