I've been investigating and I found instructions on how to create an SSL certificate with multiple hostnames, but I need to know whether I can modify an existing certificate (not create a new certificate) to allow multiple hostnames.
migrated from stackoverflow.com Nov 12 '11 at 6:50
If the certificate is self-signed (i.e. you generated it), then you can try to re-create it with existing key pair and other attributes, but even then if some application has saved hashes of the old certificate, it will complain that you have changed certificates.
If the certificate is not yours, then forget it.