qiita.js
var xpathResult = document.evaluate('descendant::text()[contains(., "キータ")]', document, null, 7, null);
for (var i = 0; i < xpathResult.snapshotLength; i++) {
var node = xpathResult.snapshotItem(i);
node.nodeValue = node.nodeValue.replace(/キータ/g, 'キター(°∀°)');
}