How do I override a JQuery (Datatable RowGroup) library function?

I'm rather new to Javascript, and the scoping syntax definitely confuses me when looking at open source libraries especially when it has a lot of advanced concepts like closure, anonymous functions, etc. The Jquery Datatables RowGroup is a a bit buggy with Responsiveness, so I took the bold attempt of writing my own attempt at a solution.

Below is the relevant snippet from the RowGroup library, source code from https://cdn.datatables.net/rowgroup/1.1.1/js/dataTables.rowGroup.js:

/** <Not sure what is going on here!> */
(function (factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD
        define(['jquery', 'datatables.net'], function ($) {
            return factory($, window, document);
        });
    } else if (typeof exports === 'object') {
        // CommonJS
        module.exports = function (root, $) {
            if (!root) {
                root = window;
            }
            if (!$ || !$.fn.dataTable) {
                $ = require('datatables.net')(root, $).$;
            }
            return factory($, root, root.document);
        };
    } else {
        // Browser
        factory(jQuery, window, document);
    }
}(function ($, window, document, undefined) {
    /** </Not sure what is going on here!> */
    'use strict';
    var DataTable = $.fn.dataTable;
    var RowGroup = function (dt, opts) {
        //...
    };
    $.extend(RowGroup.prototype, {
        //...
        _constructor: function () {
            //...
            dt.on('responsive-resize.dt', function () {
                that._adjustColspan();
            });
        },
        /** I would like to override this function, externally */
        _adjustColspan: function () {
            @ @override
        }
    });
}));

Although it is open source, instead of modifying the library directly, I'd like to override the function _adjustColspan from a separate Javascript file (which will be included after this library). This will allow the library still be update-able without hassle, and any custom changes can be easily tracked.

So I'm looking some clarification on:

1. What is this factory code above doing?
2. What is the scope of the _adjustColspan function? (From what I understand, not all functions are accessible, so what I'm trying to do might not even be possible to begin with - if it's a private function)
3. And lastly, my main question, if _adjustColspan is not a private function, how do I go about overriding it in an external .js? It does not appear to be part of the Window / global scope.