Override php module core file

With this code, you can create MODULE_NAME.php in override/modules/MODULE_NAME/ which will override the module core.

As example :
/override/modules/blocknewsletter/blocknewsletter.php :

    <?php
    class BlockNewsletterOverride extends BlockNewsletter
    {
        protected function register($email, $register_status)
    	{
                // do something
    		return parent::register($email, $register_status);
    	}
    }