Q: Changing the bullet list symbol in beamer when used from pandoc I am new to beamer . I am looking for a traditional circular bullet instead of the sideways triangle: is this possible given I am using pandoc preamble?  It seems like none of the document level  LaTeX directives can be used when pandoc is employed.
---
title: Tensorflow
documentclass: beamer
colortheme: boadilla
fonttheme: structurebold
header-includes:
  - \setsansfont{Roboto}
  - \setbeamertemplate{itemize items}[circle]
output:
    highlight: tango
  rmarkdown::html_document:
    theme: lumen
    fig_caption: yes        
---

This is being run by 
  pandoc -s -t beamer --toc-depth=5 --toc  --pdf-engine xelatex -o paper2.pdf p2.md


Update I added the header-includes with 2 beamer directives: however it had no effect.

A: The LaTeX code in your example is not correctly escaped, if you put it in the YAML block. You can fix that by creating a new file, which contains all the code, you want to add to the preamble and call pandoc with -H filename.
test.md
---
title: Test
documentclass: beamer
---


- One
    - One and a half
- Two

header.incl
\setbeamertemplate{itemize items}[circle]

Call pandoc:
$ pandoc test.md -H header.incl --pdf-engine=xelatex  -o test.pdf


