var myStyleHref = "http://tetsuya.cocolog-nifty.com/surfacetime/tetsuyalog.css";
var linkElem = document.getElementsByTagName("LINK");
for(var i = 0; i < linkElem.length; i++){
if(linkElem[i].rel == "stylesheet"){
linkElem[i].href = myStyleHref;
}
}