Reissue is a re-edition of certificate. Is the repeated issue of SSL which make a certificate available again. To reissue certificate e-mail us: email@example.com.
The proces for every Certification Authority is a slightly different. Generally speaking, for certificates that where issued for one year you will only need a new CSR file in order to reissue the SSL certificate. For SSL certificates that where purchased for terms longer than a year you will most likely have to go threw the entire validation process again.
For security reasons you should always use a new CSR for renewal.
No, the dates are coded in the certificate and cannot be changed. But you can buy a certificate valid for more than one year.