[3.1.4 modification] modify calendar library, add extra column before calendar

A library under a different name could be an option to be considered:

Code:

<?php defined('BASEPATH') OR exit('No direct script access allowed');

// application/libraries/Calendar_extra.php

if (!class_exists('CI_Calendar', false)) {
    get_instance()->load->library('calendar');
}

class Calendar_extra extends CI_Calendar {

    public function __construct($config = array()) {

        // If a configuration file is to be used,
        // its name would be calendar_extra.php

        parent::__construct($config);
    }

    // Put your customizations here.
}

Code:

// A Quick Test
        $this->load->library('calendar_extra');
        echo $this->calendar_extra->generate();