Originally Posted by hairydog2
Would this mean compiling Apache all over again? I thought there was a custom version of Apache involved, though I've never been clear why.
No you don't have to recompile anything.
ISPConfig has his own apache and you have to make the changes in the httpd.conf of ISPConfigs apache who is located in /root/ispconfig/httpd/conf/.
I think the advantage of a second webserver for the controlpanel is that the controlpanel is still rechable in case of problems with the main webserver and you can configure your own webserver the way you want and don't need to consider the special mods and configs for the controlpanel.