Update: 2021-04-18: Tweaked the code so that I could add it to the main org-export-filter-body-functions list now that I'm using Eleventy and ox-11ty.el instead of Wordpress and org2blog.

I occasionally post snippets from my Emacs configuration file, drafting the notes directly in my literate config and posting them via org2blog. I figured it might be a good idea to include a link to my config at the end of the posts, but I didn't want to scatter redundant links in my config file itself. Wouldn't it be cool if the link could be automatically added whenever I use org2blog to post a subtree from my config file? I think the code below accomplishes that.

(defun my/org-export-filter-body-add-emacs-configuration-link (string backend info)
  (when (and (plist-get info :input-file) (string-match "\\.emacs\\.d/Sacha\\.org" (plist-get info :input-file)))
    (concat string
            (let ((id (org-entry-get-with-inheritance "CUSTOM_ID")))
              (format
               "\n<div class=\"note\">This is part of my <a href=\"https://sachachua.com/dotemacs%s\">Emacs configuration.</a></div>"
               (if id (concat "#" id) ""))))))

(use-package org
  :config
  (add-to-list 'org-export-filter-body-functions #'my/org-export-filter-body-add-emacs-configuration-link))