New API for replacing an icon

app/assets/javascripts/discourse-common/lib/icon-library.js.es6

@@ -30,6 +30,9 @@ const REPLACEMENTS = {
   'notification.group_message_summary': "group"
 };
 
+export function replaceIcon(source, destination) {
+  REPLACEMENTS[source] = destination;
+}
 
 export function renderIcon(renderType, id, params) {
   for (let i=0; i<_renderers.length; i++) {

app/assets/javascripts/discourse/lib/plugin-api.js.es6

@@ -19,12 +19,12 @@ import { addUserMenuGlyph } from 'discourse/widgets/user-menu';
 import { addPostClassesCallback } from 'discourse/widgets/post';
 import { addPostTransformCallback } from 'discourse/widgets/post-stream';
 import { attachAdditionalPanel } from 'discourse/widgets/header';
-import { registerIconRenderer } from 'discourse-common/lib/icon-library';
+import { registerIconRenderer, replaceIcon } from 'discourse-common/lib/icon-library';
 import { addNavItem } from 'discourse/models/nav-item';
 
 
 // If you add any methods to the API ensure you bump up this number
-const PLUGIN_API_VERSION = '0.8.9';
+const PLUGIN_API_VERSION = '0.8.10';
 
 class PluginApi {
   constructor(version, container) {
@@ -90,6 +90,18 @@ class PluginApi {
     registerIconRenderer(fn);
   }
 
+  /**
+   * Replace all ocurrences of one icon with another without having to
+   * resort to a custom IconRenderer. If you want to do something more
+   * complicated than a simple replacement then create a new icon renderer.
+   *
+   * api.replaceIcon('d-tracking', 'smile-o');
+   *
+   **/
+  replaceIcon(source, destination) {
+    replaceIcon(source, destination);
+  }
+
   /**
    * Used for decorating the `cooked` content of a post after it is rendered using
    * jQuery.

app/assets/javascripts/discourse/widgets/notification-item.js.es6

@@ -99,8 +99,11 @@ createWidget('notification-item', {
     const lookup = this.site.get('notificationLookup');
     const notName = lookup[notificationType];
 
-    let title = I18n.t(`notifications.alt.${notName}`);
-    let icon = iconNode(`notification.${notName}`, { title });
+    let { data } = attrs;
+    let infoKey = notName === 'custom' ? data.message : notName;
+    let title = I18n.t(`notifications.alt.${infoKey}`);
+    let icon = iconNode(`notification.${infoKey}`, { title });
+
     let text = emojiUnescape(this.text(notificationType, notName));
 
     // We can use a `<p>` tag here once other languages have fixed their HTML