It worked using customize, thanks. And thanks for the explanation, Nick.
At least my approach to set the value would not work at all without an 
explicit call to org-set-emph-re, since it relied on the variable being 
already defined.
It might be of minor interest, anyway, I've attached a patch-suggestion 
that would clearify the usage sufficiently, at least for me...

Best regards, Philipp


On Fri, Aug 17, 2012 at 03:50:35PM -0400, Nick Dokos wrote:
> Sebastien Vauban <wxhgmqzgwmuf@spammotel.com> wrote:
> 
> > You have to make that customization *before* loading Org in your .emacs file.
> > Weird, never really understood why, but that's like that.
> > 
> 
> The point is that the value of org-emphasis-alist (as well as the value
> of org-emphasis-regexp-components) is used in order to calculate the
> value of org-emph-re by calling the function org-set-emph-re afterwards:
> it's org-emph-re that's used for the all the gory calculations, not
> org-emphasis-alist, which just provides a nicer interface.
> 
> So if you arrange to call the org-set-emph-re function afterwards, you
> can change org-emphasis-alist at any time. Customize makes it easy, in
> that it does that automatically (see the :set property
> of org-emphasis-alist).
> 
> If you do the setq before loading org, then what happens is that when the
> defcustom is encountered, the value of the :set property (a function) is
> called: the modified value of org-emphasis-alist is then used to calculate
> org-emph-re, instead of the original default. If you do it after, none
> of that happens and it's as if you never changed it.
> 
> Nick
> 
> PS BTW, the docstring for the variable says: "Use customize to modify
>    this, or restart Emacs after changing it" but I'm not sure that's
>    correct: if you change the variable in one session, the value is not
>    going to be propagated to the next session, unless you use customize
>    or put the setq in .emacs. In the latter case, it's not going to work
>    unless you do it the way Seb describes: set it before loading Org.
>    So restarting emacs is *not* enough. Am I missing something?
> 
>