Manipulate the DOM with jQuery just before the page loads

Question

Because of accesibility tests i need to manipulate the html of my page just before it loads completely. I dont want to manipulate contrib modules i am using, so i need to do it with jQuery. In fact, i think the way i'm doing it changes the page when it loads completely so the online accesibility tools i use don't see my changes. I'm using the following:

  Drupal.behaviors.bcsc = {
    attach: function (context, settings) {
      $(document).ready(function () {
              /******/
              //here my code
              /******/
      },//end function
    };//end behaviour
})(jQuery, Drupal);

will changing $(document).ready(function () for $(document).beforeReady(function () work?