How to change mailing form and set the default value for url_tracking to false?
Disclaimer: I'm not an angularjs expert

Again this is a bit of a hack, we are intercepting a built-in CiviCRM angular directive and extending to add behaviour.

Create a custom extensions or use an existing one and implement hook_civicrm_angularModules:

function myextension_civicrm_angularModules(&amp;$angularModules){
        $angularModules['myModule'] = array(
                'ext' =&gt; 'myextension',
                'js' =&gt; array('js/myModule.js'),
        );
}


In your js file:

// js/myModule.js

(function(angular, $, _){
  // Your module
  angular.module('myModule', []);

  // the hack
  angular.module('crmMailing').config(function($provide){

    // crmMailingBlockTracking directive
    $provide.decorator('crmMailingBlockTrackingDirective', function($delegate){
        var directive = $delegate[0];

        // Original link function
        var link = directive.link;

        // compile function, returns new link function
        directive.compile = function(){
            return function(scope, element, attrs){
                // get old link functionality
                link.apply(this, arguments);

                // new functionality here
                scope.$parent.$watch(attrs.crmMailing, function(){
                    var createdDate = new Date(scope.mailing.created_date).getTime()/1000;
                    var nowDate = new Date().getTime()/1000;

                    if((nowDate - createdDate) &lt; 60){
                        scope.mailing.url_tracking = '0';
                        CRM.alert('Tracking Disabled');
                    }

                }); 
            };
        };

        return $delegate;
    });
  });
})(angular, CRM.$, CRM._);


The angular Mailing app uses a kind of boilerplate service, crmMailingSimpleDirective for constructing directives see here more info

The above snippet will do the same as my other answer without relying on setTimeout().

Hope that helps.