Thanks so much! I was trying to get a bit more flexibility with that
separate slide (e.g., have the title in the centre of the page and no toc).
So I took inspiration from your great solution and defined a latex macro

#+begin_src latex
\newcommand{\singleslide}[1]{{%
    \usebeamerfont{title}
    \begin{frame}[plain,c]
      \begin{center}
        \begin{minipage}[h]{.75\textwidth}
          \centering
          \textcolor{title}{\Large#1}
      \end{minipage}
      \end{center}
    \end{frame}
}}
#+end_src

and a latex class

#+begin_src emacs-lisp
(add-to-list 'org-latex-classes
                  '("my-org-beamer"
                    "\\documentclass{beamer}

("\\singleside{%s}" . "\\singleslide{%s}")))))
#+end_src

which did the job.

Best,
  Seb

On Sat, Apr 26, 2014 at 9:05 AM, Eric S Fraga <e.fraga@ucl.ac.uk> wrote:

> On Friday, 25 Apr 2014 at 08:24, Seb Frank wrote:
> > Hi there,
> >
> > I have customized org-beamer--format-frame to change the way headlines
> are
> > treated (as I want a separate slide with only the headline in the center
> > and plain frames not showing headlines after that). The way I currently
> do
> > this is by redefining the function itself (using "defun
> > org-beamer--format-frame"). This works, but is there any way to make this
> > more modular, i.e. tell org-mode somewhere to use a different function
> > (e.g., my-org-beamer--format-frame) to format a frame, so that it's easy
> to
> > switch back and forth between different ones, as well as to revert to the
> > default?
> >
> > Thanks,
> >   Seb
>
> As you haven't explained why you want this, it's difficult to understand
> the actual use case.  So, guessing at your intent, I wonder whether you
> have thought about making use of section headings as well as frame
> headings to accomplish what you want?
>
> Assuming you are using org v8.x and not something older, if you set
> option H:2, second level headings define frames and top level headings
> define sections.  You can then have section headings appear as a
> separate slide using code such as this:
>
> #+begin_src org
>   ,#+latex_header:
> \AtBeginSection[]{\begin{frame}<beamer>\frametitle{Topic}\tableofcontents[currentsection]\end{frame}}
> #+end_src
>
> In this case, any time a section heading is encountered (i.e. top level
> org heading), you'll get a slide with a table of contents with that
> heading emphasised.  You can obviously do something different which more
> closely matches what you want.
>
> If you don't want individual frames to have headings, simply don't put
> any text in the headline for that frame.
>
> This way, you do not need to manipulate how beamer displays frames.  An
> example set of slides with two sections and two out of four slides
> having no headline would look like this:
>
> #+begin_src org
>   ,#+options: H:2
>   ,#+latex_header:
> \AtBeginSection[]{\begin{frame}<beamer>\frametitle{Topic}\tableofcontents[currentsection]\end{frame}}
>   ,* Introduction
>   ,** First slide
>   some text on the first slide
>   ,**
>   some text on the second slide which has no heading
>   ,* Results
>   ,**
>   some third slide text, also on a slide with no heading
>   ,** conclusions
>   This was a great talk.
> #+end_src
>
> HTH,
> eric
> --
> : Eric S Fraga (0xFFFCF67D), Emacs 24.4.50.2, Org
> release_8.2.5h-1027-g4c0a29
>