mefi-reorder-signature.user.js

// ==UserScript==
// @name          Metafilter comment signature reordering
// @namespace     mefireordersignature
// @description   
// @include       http://*.metafilter.com/*
// @include       https://*.metafilter.com/*
// @version       0.0.1
// @grant         none
// ==/UserScript==

// get all the signatures denoted by the smallcopy class
$(".comments > .smallcopy").each(function() {
  var contents = $(this).contents(); // the contents of this smallcopy span
  var topSpan = $("<span>"); // the new span we'll be placing at the top of the comment
  
  for (var i = 0; i < contents.length; i++) {
    var node = contents[i];
    // discard the "posted by" node
    if (node.nodeType == 3 && node.textContent.trim() == "posted by") {
      $(node).detach();
      continue;
    }
    // check if we've reached the "at" node
    if (node.nodeType == 3 && node.textContent.trim() == "at") {
      // get rid of it
      $(node).detach();
      // then stop: everything after it stays in place
      break;
    }
    // this is before the "at" node so add it to our new span
    topSpan.append(node);
  }

  // add " posted:" at the end of the new span
  topSpan.append(" posted:");
  // assign the same smallcopy class for styling
  topSpan.addClass("smallcopy");

  // place it at the beginning of the comment div
  $(this).parent().prepend(topSpan);
});