[Vitaly Po]

Если так?

function modifyClass(className,func,param){
var objecs = document.getElementsByClassName(className);

for(i=0; i<objecs.length; i++){
	var id = objecs[i].id;

	if(func == 'renameClass'){
		document.getElementById(id).className = param;
		if( objecs.length > 0 ){
			modifyClass(className,func,param);
		}
	}
}
}

function modifyClass('xxx','renameClass','yyy')