Use cases:

### Adding post-update hooks, which requires diverting Ikiwiki's hook.

    mv /srv/git/poop.git/hooks/post-update /srv/git/poop.git/hooks/post-update-ikiwiki
    cat > /srv/git/poop.git/hooks/post-update
      #!/bin/sh
      /srv/git/poop.git/hooks/post-update-ikiwiki &
      echo This is a hook that does things!
    cat > /srv/ikiwiki/piny/poop.setup.pl
      foreach(@{$conf->{wrappers}}) { $_->{wrapper} =~ s/post-update/post-update-ikiwiki/; };
    rebuildrepo poop

### Adding or removing plugins, or plugin confuration variables.

    cat > /srv/ikiwiki/piny/poop.setup.pl
      push(@{$conf->{add_plugins}}, 'txt');
    rebuildrepo poop

### Any other special confuration requests from hosted projects.

    cat > /srv/ikiwiki/piny/poop.setup.pl
      $conf->{teximg_prefix} .= "\n\\newcommand{\\unit}[1]{\\ensuremath{\\, \\mathrm{#1}}}"
    rebuildrepo poop