I mean to put this in your init file:

(add-to-list 'org-latex-classes
             '("xxllp"
               "\\documentclass[oumk,xs]{xxllp}
 [NO-DEFAULT-PACKAGES]
 [NO-PACKAGES]
\\usepackage{amsmath}
\\usepackage{amssymb}
\\usepackage{blabla}
\\usepackage{blablabla}
\\pagestyle{myheadings}\\markboth{Author}{Title of the paper}
"
       ("\\section{%s}" . "\\section*{%s}")
       ("\\subsection{%s}" . "\\subsection*{%s}")
       ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
       ("\\paragraph{%s}" . "\\paragraph*{%s}")
       ("\\subparagraph{%s}" . "\\subparagraph*{%s}")))


And then in your org file:

#+latex_class: xxllp
#+options: toc:nil

#+BEGIN_EXPORT latex
\\LaLPonline{??} \\setcounter{page}{1} \\thispagestyle{LLPrrobezissn}
\\label{p}
\AuthorTitle{Joseph Vidal-Rosset}{\uppercase{Title of the paper}}
#+END_EXPORT

plus rest of your document. That exports as:

% Created 2018-06-11 Mon 09:50
% Intended LaTeX compiler: pdflatex
\documentclass[oumk,xs]{xxllp}
 \usepackage{amsmath}
\usepackage{amssymb}
\usepackage{blabla}
\usepackage{blablabla}
\pagestyle{myheadings}\markboth{Author}{Title of the paper}
\author{John Kitchin}
\date{\today}
\title{}
\begin{document}

\\LaLPonline{??} \\setcounter{page}{1} \\thispagestyle{LLPrrobezissn}
\\label{p}
\AuthorTitle{Joseph Vidal-Rosset}{\uppercase{Title of the paper}}

the rest of your document...

\end{document}




John

-----------------------------------
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu


On Mon, Jun 11, 2018 at 8:29 AM, Joseph Vidal-Rosset <
joseph.vidal.rosset@gmail.com> wrote:

> Le lun. 11 juin 2018 à 07:23:54 , John Kitchin <jkitchin@andrew.cmu.edu>
> a envoyé ce message:
> > Why can’t you just put that last one in your org file?
>
> Dear John,
>
> I confess  that I  do not  understand the solution  you suggest.  Do you
> suggest to me to put all the headers of this class in an org file?
> Sorry to be so slow.
>
> Best wishes,
>
> --
> Joseph
>