one option is to use a getElementByClassName function and then loop through the returned element objects and change their className to whatever you need.
function getElementsByClassName(oElm, strTagName, strClassName) {
var arrElements = (strTagName == "*" && oElm.all)? oElm.all : oElm.getElementsByTagName(strTagName);
var arrReturnElements = new Array();
strClassName = strClassName.replace(/\\-/g, "\\\\-");
var oRegExp = new RegExp("(^|\\\\s)" + strClassName + "([\\\\s|$](file:///s:$))");
var oElement;
for(var i=0; i<arrElements.length; i++)
{
oElement = arrElements[i];
if(oRegExp.test(oElement.className))
{
arrReturnElements.push(oElement);
}
}
return (arrReturnElements)
}
//example usage
var divObjs = getElementsByClassName(document,'div','myClass');