<script type="text/javascript">
jQuery(document).ready(function(){
jQuery('input[name=go]').val('Search');
});
</script>
There is a lag...but it will replace the text value of an input field if you do not have access to the html.
<script type="text/javascript">
jQuery(document).ready(function(){
jQuery('input[name=go]').val('Search');
});
</script>