copy all code from original source, include it in new module. apply sequence to change load order if needed. do your modifications where needed. re-generated assets and done.

'use strict';
odoo.define('your_module_name.checkout', function (require) {

    require('web.dom_ready');
    var ajax = require('web.ajax');

    var _onCarrierClick = function(ev) {
        $pay_button.prop('disabled', true);
        var carrier_id = $(ev.currentTarget).val();
        var values = {'carrier_id': carrier_id};
        ajax.jsonRpc('/shop/update_carrier', 'call', values)
          .then(_onCarrierUpdateAnswer);
    };

    var $carriers = $("#delivery_carrier input[name='delivery_type']");
    $carriers.click(_onCarrierClick);
    // diy: avoid double ajax calls!