info: will only work for systems that use apache2 like most linux ones (path to httpd.conf may vary depending on OS)
check if httpd.conf
exists
ls /etc/apache2/httpd.conf
open it and scroll to bottom of file:
cat /etc/apache2/httpd.conf
you should see some include like Include /private/etc/apache2/other/*.conf
that will include all configs from that certain path.
let's create extra config: (switch to root)
echo '<IfModule mod_headers.c> Header append HEADER_NAME "VALUE" </IfModule>' > /private/etc/apache2/other/extraheader.conf