Overriding config.php ?

[eluser]Unknown[/eluser]
This is my config.php file xss filtering setting.

Code:

$config['global_xss_filtering'] = TRUE;

I would like to change it on runtime as

Code:

$config['global_xss_filtering'] = FALSE;

This function is not working.

Code:

$this->config->set_item('global_xss_filtering', FALSE);

Is it possible? How?