Inserting \usepackage{xparse} before citeproc command definition in LaTeX preamble

[wuffi]

Is there a way to include a LaTeX package before citeproc-related definitions in the preamble of LaTeX output generated by Pandoc:

Running pandoc with the citeproc option puts a \NewDocumentCommand\citeproc{}{} definition into the preamble of the LaTeX output.
The macro \NewDocumentCommand is defined by the xparse LaTeX package (but also directly in the LaTeX kernel of newer LaTeX versions).
The xparse package gets not included in the preamble with my versions of Pandoc and Citeproc and thus compilation with LaTeX fails.
Including LaTeX packages is easy with Pandoc, but they would only appear after citeproc-related definitions in the preamble of the *.tex file generated by Pandoc.

[badumont]

You can always use a custom LaTeX template: run `pandoc -D latex` to get the default template used by pandoc, modify it, and use your custom version with the --template command line option. Older LaTeX installations could be made to work out of the box by adding to the template something like: ***@***.***{NewDocumentCommand}{\usepackage{xparse}}{}`.

[wuffi]

Thanks, using a custom template is probably indeed the cleanest solution.
I was a bit afraid and thus hesitant to do so, but starting from Pandoc's default one, it is quite feasible and actually easy to adjust it.