Fijate si te sirve este ejemplo sencillo:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento sin título</title>
<script>
function hacerAlgo(p){
alert(p);
}
</script>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<input id="campo" type="text" name="textfield" onchange="hacerAlgo(123)" />
<input type="button" name="Submit" value="remover" onclick="document.getElementById('campo').onchange=null;" />
<input name="restituir" type="button" id="restituir" value="restituir" onclick="document.getElementById('campo').onchange=function(){hacerAlgo(123);}" />
</form>
</body>
</html>