Removing items from context menu

When you define the menu item, you can add it to an existing group if you want:
IE
group: 'image' //have to be added in config

would add the item to the image group, and would appear where the image context item currently is. Unforunately I don't remember where the groups are defined off-hand. You can always look at the plugin definition of the plugin you want to put it next to and do it that way.

As for removing listeners, I assume you don't want to remove the actual plugin. So I looked at the contextxmenu plugin, and it doesn't appear that the prototype allows for the removal of items, but you could look at the this._.listeners variable and maybe destroy them manually there. You'd have to loop through them though, and since they are anonomous functions...that could get very tricky. If you end up doing that, share your code as I'm sure many others would be interested.

I had a similar issue and I decided to dig into editor.contextMenu using Firebug. I found out something that looked promising and after few quick tests, I found the following to work for my needs.

if(editor.contextMenu) {
   editor.contextMenu.addListener(function(element, selection) {
      // I want my context item only on elements with certain class name
      if(!element.hasClass('someClass')) {
         return null;
      }
      editor.contextMenu.removeAll(); // this line removes all entries from the context menu
      return {
         someCommandName : CKEDITOR.TRISTATE_ON
      };
   });
}