Modifying a existing SSL cert on SBS 2003/ IIS 6

Hi, I was just wondering how you modify an existing SSL cert on SBS 2003. The current one that work is using is causing problems as the address it uses is the server’ domain name and this is conflicting with the public url for external mail access.

Is it possible to modify the current cert or do you have to remove it and redeploy a new one?
Also would this in any way effect comunication with the ISP?

Thanks,
Ger