The configuration files for the HTTP deamon can be found in:
/etc/httpd/conf
Several configuration files are recreated when you restart the HTTP service, so pay attention to which files are going to be edited.
The ‘source’ for the httpd.conf is httpd.conf-user in /usr/syno/apache/conf. But it might be cleaner to edir one of the included config files inside the /etc/httpd/conf/extra directory
The HTTP deamon can be restarted with:
/usr/syno/sbin/synoservicecfg --restart httpd-user /usr/syno/sbin/synoservicecfg --restart httpd-sys
There are more services that can be restarted with the same tool. For a complete list, look at
/usr/syno/sbin/synoservicecfg --list