下記のソースコードは、"文字マウスストーカー"のメッセージ内容を
selectのoptionタグで変えようとしたものですが、メッセージ自体は
切り替わるのですが、マウスストーカーの効果が失われてしまいます。
この効果が失われないでメッセージ内容を変えるには、どうすればいいでしょうか。

<!DOCTYPE html>
<html lang="ja">
<head>
<meta http-equiv="Content-type" content="text/html; charset=Shift_JIS">
<meta http-equiv="Content-Script-Type" content="text/javascript">
<meta http-equiv="Content-Style-Type" content="text/css">
<title>文字マウスストーカー</title>

<style type="text/css">
<!--
#myText {
font-style: italic;
font-weight: bold;
font-family: 'comic sans ms', verdana, arial;
color: #ff0000;
position: absolute;top: 0;left: 0;z-index: 3000;cursor: default;}
#myText div {position: relative;}
#myText div div {position: absolute;top: 0;left: 0;text-align: center;}
//-->
</style>


<script type="text/javascript">
<!--

function message(opt){
　　　　　　document.getElementById('myText').innerHTML= opt.options[opt.selectedIndex].value;
}
;(function(){
var msg="ご入学おめでとう！";
var size = 24;
var circleY = 0.75; var circleX = 2;
var letter_spacing = 5;
var diameter = 10;
var speed = 0.3;
var rotation = 0.4;
if (!window.addEventListener && !window.attachEvent || !document.createElement) return;

msg = msg.split('');
var n = msg.length - 1, a = Math.round(size * diameter * 0.208333), currStep = 20,
ymouse = a * circleY + 20, xmouse = a * circleX + 20, y = [], x = [], Y = [], X = [],
o = document.createElement('div'), oi = document.createElement('div'),
b = document.compatMode && document.compatMode != "BackCompat"? document.documentElement : document.body,

mouse = function(e){
 e = e || window.event;
 ymouse = !isNaN(e.pageY)? e.pageY : e.clientY; // y-position
 xmouse = !isNaN(e.pageX)? e.pageX : e.clientX; // x-position
},

makecircle = function(){ // rotation/positioning
 if(init.nopy){
  o.style.top = (b || document.body).scrollTop + 'px';
  o.style.left = (b || document.body).scrollLeft + 'px';
 };
 currStep -= rotation;
 for (var d, i = n; i > -1; --i){ // makes the circle
  d = document.getElementById('iemsg' + i).style;
  d.top = Math.round(y[i] + a * Math.sin((currStep + i) / letter_spacing) * circleY - 15) + 'px';
  d.left = Math.round(x[i] + a * Math.cos((currStep + i) / letter_spacing) * circleX) + 'px';
 };
},

drag = function(){ // makes the resistance
 y[0] = Y[0] += (ymouse - Y[0]) * speed;
 x[0] = X[0] += (xmouse - 20 - X[0]) * speed;
 for (var i = n; i > 0; --i){
  y[i] = Y[i] += (y[i-1] - Y[i]) * speed;
  x[i] = X[i] += (x[i-1] - X[i]) * speed;
 };
 makecircle();
},

init = function(){ // appends message divs, & sets initial values for positioning arrays
 if(!isNaN(window.pageYOffset)){
  ymouse += window.pageYOffset;
  xmouse += window.pageXOffset;
 } else init.nopy = true;
 for (var d, i = n; i > -1; --i){
  d = document.createElement('div'); d.id = 'iemsg' + i;
  d.style.height = d.style.width = a + 'px';
  d.appendChild(document.createTextNode(msg[i]));
  oi.appendChild(d); y[i] = x[i] = Y[i] = X[i] = 0;
 };
 o.appendChild(oi); document.body.appendChild(o);
 setInterval(drag, 25);
},

ascroll = function(){
 ymouse += window.pageYOffset;
 xmouse += window.pageXOffset;
 window.removeEventListener('scroll', ascroll, false);
};

o.id = 'myText'; o.style.fontSize = size + 'px';

if (window.addEventListener){
 window.addEventListener('load', init, false);
 document.addEventListener('mouseover', mouse, false);
 document.addEventListener('mousemove', mouse, false);
  if (/Apple/.test(navigator.vendor))
   window.addEventListener('scroll', ascroll, false);
}
else if (window.attachEvent){
 window.attachEvent('onload', init);
 document.attachEvent('onmousemove', mouse);
};
})();

// -->
</script>

</head>
<body bgcolor="#ccffff">
<div style="text-align:center">
<select onchange="message(this)">
<option style="background-color:lightskyblue;font-weight:bold" value="ご入学おめでとう！" selected>メッセージ１</option>
<option style="background-color:yellow;font-weight:bold" value="誕生日おめでとう！">メッセージ２</option>
</select>
</div>
</body>
</html>