var bT = document.evaluate( '//td[@class="bodytext"]' ,document, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null );

for (var i = 0; i < bT.snapshotLength; i++){

	bT.snapshotItem(i).textContent = bT.snapshotItem(i).textContent.replace(/poo/gim,'ass');

}