Question

When I do C-c C-e l to export an Org file to LaTeX it produces a document with a particular preamble. Instead of this particular preamble I would like it to use a preamble of my choice. Say that I want it to use the following preamble:

% Don't forget to qpdf --linearize the final copy
\RequirePackage[l2tabu,orthodox]{nag}% Old habits die hard. All the same, there are commands, classes and packages which are outdated and superseded. nag provides routines to warn the user about the use of those.
\immediate\write18{sh ./vc}
\input{vc}% Version control macros (for \VCDateISO in \date) http://www.ctan.org/pkg/vc
\documentclass[a4paper,12pt]{article}% pt? doublepage?
%\usepackage{geometry}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}% Latin Modern (derivate of Knuth's CM)
\usepackage{fixltx2e}% \textsubscript and bugfixes for LaTeX
\usepackage{microtype}
\usepackage[strict=true]{csquotes}% Context-sensistive quotes. \enquote "" \enquote* ''. Use the integrated commands \textcquote and \blockcquote rather than biblatex internal commands to get contex sensistive quotes for them too. s/babel/autostyle in new version.
\usepackage[bookmarks,pdfborder={0 0 0}]{hyperref}% links and pdfinfo. MUST BE LOADED LAST!

\hypersetup{% Setup for hyperref
pdftitle    = {[Title from #+TITLE]},
pdfauthor   = {[Author from #+AUTHOR]}
}

I know that you can manipulate which packages are used on a per file basis as described in the manual but I want this preamble to be used for all files unless ) specify otherwise. The preamble I want to use includes the following:

• deactivated packages (such as geometry above)
• packages loaded by RequirePackage
• input macros
• \immediate\write18 macros
• comments after usepackage macros
• a hypersetup macro that recognizes #+TITLE and #+AUTHOR from Org-mode files

Answer 1

Deactivated packages (such as geometry above)

Org-mode recognizes LaTeX syntax inside LaTeX code-blocks, as well as when including LaTeX files in the content. (See Quoting LaTeX code.)

Packages loaded by RequirePackage

As above.

Input macros

As above.

\immediate\write18 macros

I believe this should also be as above, however there is an alternate method of dealing with this. If you create a source code block of type sh with the command within it, Org will evaluate it on export and produce the desired behaviour. You have to enable sh as a babel language type for it to work however.

(require 'ob-shell)

You can also include sh as one of the languages loaded by babel by adding it to org-babel-load-languages

(acons 'sh 't org-babel-load-languages)

Then use a code block similar to the following to run your ./vc

#+name: Test
#+begin_src sh :results output silent :exports results
  ./vc
#+end_src

As long as this comes before your \input{vc} line it should run the code and then include it. Simply follow the code-block with

#+LATEX: \input{vc}

And your content should be included.

Comments after usepackage macros

If the code is within a LaTeX block it should recognize it as LaTeX.

A hypersetup macro that recognizes #+TITLE and #+AUTHOR from Org-mode files.

This will have to be included within each document rather than separate. The following will provide what you desire for your macros. It will not be within the preamble, however it will end up at the top of the document and the export does behave as expected (however it will not behave as expected if added through #+INCLUDE: from org.

#+begin_latex
  \hypersetup{% Setup for hyperref
  pdftitle    = {{{{TITLE}}}}, %Org macro to take from #+TITLE
  pdfauthor   = {{{{AUTHOR}}}} %Org macro to take from #+AUTHOR
  }
#+end_latex

Creating your own Latex export class

If you follow the instructions in the worg tutorials (See Org Latex Export) you can create your own export-class. If you want to have full control over the packages in the preamble you would simply need to:

(add-to-list 'org-export-latex-classes
             '("<CLASS NAME>"
               "\\documentclass{article}
               [NO-DEFAULT-PACKAGES]
               [NO-PACKAGES]"
               <insert desired sectioning configuration>))

You can also add in your desired packages between the \\documentclass and [NO-DEFAULT-PACKAGES] lines. The alternative would be to add them to the file itself using:

#+LATEX_CLASS: <CLASS NAME>
#+LATEX_HEADER: \usepackage{package}
...

As a third option, you can simply create a custom .sty file with the desired packages etc and include it as a single #+LATEX_HEADER:.