Untitled

<html>
    <body>
       <div>
         <script src="myfile1.js"></script>
       </div>
       <div>
         <script src="myfile1.js"></script>
       </div>
    </body>
 </html>

var scripts = document.getElementsByTagName ( "script" );
var l = scripts.length;
for ( var i = 0; i < l; ++ i )
{
   if ( scripts [i].src = "myfile1.js" )
   {
      scripts [i].parentNode.innerHTML = "new content";
   }
}

<html>
    <head>
        <!-- I recommend getting this from Google Ajax Libraries
             You don't need this, but it makes my answer way shorter -->
        <script type="text/javascript" src="jquery.js"></script>
        <script type="text/javascript">
          $(document).ready(function(){
             function getRandomContent(){
              // I expect this is the contents of your current script file.
              // just package it into a function.
              var rnd = Math.random();
              return "[SomeHtml]";
             }
             $('.random').each(idx, el){
                 $(this).html(getRandomHtmlContent());
             });
          });
        </script>
    </head>
    <body>
       <div class="random">
       </div>
       <div class="random">
       </div>
    </body>
 </html>