All server with CWP can have custom php.ini file set per user account or per folder.
User can manually create php.ini file and add values which needs to be changed in it.

Location of the global server php.ini file is
/usr/local/php/php.ini

Location of the global per account php.ini file is
/home/USERNAME/php.ini

You can also have per folder changes, example:
/home/USERNAME/public_html/website1.com/php.ini
/home/USERNAME/public_html/website2.com/php.ini
/home/USERNAME/public_html/website2.com/myapp/php.ini

How to test php.ini changes?
Simple create phpinfo.php file in the users public_html folder and add the following content in it.

Example location: /home/USERNAME/public_html/phpinfo.php
<?php
phpinfo();
?>
Now open url in your browser (Apache restart is NOT needed):

http://your-domain.com/phpinfo.php

PHP.ini values

http://php.net/manual/en/ini.list.php