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}