toggle-file-as-root.el

(defun toggle-alternate-file-as-root (&optional filename)
  "Toggle between the current file as the default user and as root."
  (interactive)
  (let* ((filename (or filename (buffer-file-name)))
         (parsed (when (tramp-tramp-file-p filename)
                   (coerce (tramp-dissect-file-name filename)
                           'list))))
    (unless filename
      (error "No file in this buffer."))

    (find-alternate-file
     (if (equal '("sudo" "root") (butlast parsed 2))
         ;; As non-root
         (if (or
              (string= "localhost" (nth 2 parsed))
              (string= (system-name) (nth 2 parsed)))
             (nth -1 parsed)
           (apply 'tramp-make-tramp-file-name
                  (append (list tramp-default-method nil) (cddr parsed))))

       ;; As root
       (if parsed
           (apply 'tramp-make-tramp-file-name
                  (append '("sudo" "root") (cddr parsed)))
         (tramp-make-tramp-file-name "sudo" "root" nil "localhost" nil filename))))))