Change an element's onfocus handler with Javascript?

function clear_input(element)
{
    element.value = "";
    element.onfocus = null;
}

function restore_default(element)
{
    if(element.value == '')
    {
        element.value = element.name.substring(0, 1).toUpperCase()
                          + element.name.substring(1, element.name.length);
    }
}

element.onfocus = "javascript:clear_input(this);";

element.onfocus = clear_input;

element.onfocus = function () {
    clear_input( param, param2 );
};

function clear_input () {
    this.value = "";
    this.onfocus = null;
}

function trim(str) {
    return str.replace(/^ss*/, '').replace(/ss*$/, '');
}

function capitalize(str) {
    return str.substr(0, 1).toUpperCase() + str.substr(1).toLowerCase();
}

function clear_default(element) {
    if (trim(element.value) == element.defaultValue ) { element.value = ""; }
}

function restore_default(element) {
    if (!trim(element.value).length) { element.value = element.defaultValue;}
}

function hightlight_input(element) {
    element.select();
}

function restore_default(element) // optional, do we restore if the user deletes?
{
    if(element.value == '')
    {
        element.value = element.name.substring(0, 1).toUpperCase()
                          + element.name.substring(1, element.name.length);
    }
}

<!-- JavaScript
function checkClear(A,B){if(arguments[2]){A=arguments[1];B=arguments[2]} if(A.value==B){A.value=""} else if(A.value==""){A.value="Search"}}
//-->

<form method="post" action="search.php">
<input type="submit" name="1">
<input type="text" name="srh" Value="Search" onfocus="checkClear(this,'Search')" onblur="checkClear(this,' ')">
</form>