I have setup ispconfig3 with aaa.domain.com. So I can use aaa.domain.com to access the control panels and so on. Now, I would like to change this domain name to bbb.another.com. Is that possible? How deep is the default domain name tied to ispconfig3? How important is this domain name to ispconfig3? Thanks.
ISPCOnfig does not use the default domain name. It is only used in the server settings to identify the server. The system part that relies on that name is postfix, so you will have to change the name in the following files (if exists): /etc/postfix/main.cf /etc/mailname /etc/hostname /etc/hosts and then restart postfix and amavisd.
If you simply want to access the control panel from another domain, you can do that easily. You can use any of your domains hosted on your server: Http://anyhosteddomain.com:8080