How to use a custom pandoc HTML template in bookdown::gitbook

I'd like to write a custom template for a bookdown project. From the documentation of the bookdown package I read that it is possible to replace the default template with a custom one, say my_custom_template.html, by including template: "my_custom_template.html" in the YAML header like

bookdown::gitbook:
  template: my_custom_template.html

Doing so yields the following error:

Error in rmarkdown::html_document(..., extra_dependencies = c(extra_dependencies,  : 
  formal argument "template" matched by multiple actual arguments
Calls: <Anonymous> ... do.call -> <Anonymous> -> html_document2 -> <Anonymous>
Execution halted
Error in eval(expr, envir, enclos) : 
  Failed to compile the book to bookdown::gitbook

It seems to me that the default template is hardcoded and thus cannot be overriden that easily.

Is there another way to include a custom template?

Solution

Update: This has become possible since bookdown v0.8 (thanks to the PR #570).

This is not possible, and it is documented this way: In the documentation for the used function (?bookdown::gitbook) template is excluded from the list of available parameters to be passed to rmarkdown::html_document(), along with toc and theme. This is also mentioned in the page you are linking to:

There are a few arguments of html_document() that have been hard-coded in gitbook() and you cannot change them: toc = TRUE (there must be a table of contents), theme = NULL (not using any Bootstrap themes), and template (there exists an internal GitBook template).