Auto generation of php.ini

Auto generation of php.ini

In my phpinfo I see this:
Configuration File (php.ini) Path /etc
Loaded Configuration File /var/www/vhosts/example.com/etc/php.ini
Scan this dir for additional .ini files /etc/php.d
When I open /var/www/vhosts/example.com/etc/php.ini file, I see this notice:
; ATTENTION! ;
; DO NOT MODIFY THIS FILE BECAUSE IT WAS GENERATED AUTOMATICALLY,
; SO ALL YOUR CHANGES WILL BE LOST THE NEXT TIME THE FILE IS GENERATED.
When I change this file and make service httpd restart, I see that phpinfo
changed. But what can I do for permanent change ?
When I change /etc/php.ini file and restart httpd, I see that the values
didn't change. It seems like php.ini file isn't auto generated when httpd
is restarted.
What triggers auto generation ?
System: Centos 6.3, Plesk 11, PHP 5.4.17