R Markdown with Tex Header - r

Question

I have created a LaTeX header file for assignments to make my R Markdown convert to PDF as desired. The header file works perfectly but has a couple of defined commands to give my name, assignment number/name and the class name.
\newcommand{\hmwkAuthorName}{Joe Bloggs}
\newcommand{\hmwkClass}{CompSci 101}
\newcommand{\hmwkTitle}{Assignment Numero Uno}
I want to be able to define these in the YAML section of my R Markdown but always getting "Undefined Control Sequence" and error 43 when converting which is remedied by putting these sections back in the header file.
This is what the YAML section looks like currently (not working):
---
title: "Assignment Numero Uno"
author: "Joe Bloggs"
header-includes:
- \newcommand{\hmwkAuthorName}{Joe Bloggs}
- \newcommand{\hmwkClass}{CompSci 101}
- \newcommand{\hmwkTitle}{Assignment Numero Uno}
output:
pdf_document:
includes:
in_header: header_temp.tex
---
How can I achieve this?
EDIT: The full header file is
\usepackage{fancyhdr}
\usepackage{lastpage}
\topmargin=-0.45in
\evensidemargin=0in
\oddsidemargin=0in
\textwidth=6.5in
\textheight=9.0in
\headsep=0.25in
\linespread{1.1}
\pagestyle{fancy}
\lfoot{\hmwkAuthorName}
\chead{\hmwkClass:\ \hmwkTitle}
\lhead{}
\cfoot{}
\rfoot{Page\ \thepage\ of\ \protect\pageref{LastPage}}
\renewcommand\headrulewidth{0.4pt}
\renewcommand\footrulewidth{0.4pt}
\setlength\parindent{0pt}
\title{
\vspace{2in}
\textmd{\textbf{\hmwkClass:\ \hmwkTitle}}\\
\vspace{3in}
}
\author{\textbf{\hmwkAuthorName}}
\date{}