How do you change the font size globally for the \texttt environment?
I can do it for the verbatim environment with the following pair of commands
\newcommand{\verbatimfont}[1]{\renewcommand{\verbatim@font}{\ttfamily#1}}
\verbatimfont{\small}
How do I accomplish the same thing for the \texttt environment?
Font switches are typically robust. You could update the \ttfamily font switch to append a sizing element to it in the same way you would for your \verbatimfont:
\documentclass{article}
\usepackage{letltxmacro}
% https://tex.stackexchange.com/q/88001/5764
\LetLtxMacro\oldttfamily\ttfamily
\DeclareRobustCommand{\ttfamily}{\oldttfamily\csname ttsize\endcsname}
\newcommand{\setttsize}[1]{\def\ttsize{#1}}%
\begin{document}
\setttsize{\Large}% \ttfamily will be \Large
Something \texttt{texttt}.
\begingroup
\ttfamily Something texttt.
\endgroup
\setttsize{}% \ttfamily will be \normalsize
Something \texttt{texttt}.
\begingroup
\ttfamily Something texttt.
\endgroup
\end{document}
You can use the fancyvrb package that offers many other customizations (you can also check the fvextra package that adds many features).
\documentclass{article}
\usepackage{fancyvrb}
\RecustomVerbatimEnvironment{verbatim}{Verbatim}{fontsize=\footnotesize}
\begin{document}
This is inline \verb|verbatim|, the size doesn't change.
But it can be changed when we are in a \verb|verbatim|
enviroment
\begin{verbatim}
This is inline \verb|verbatim|, the size doesn't change.
But it can be changed when we are in a \verb|Verbatim|
enviroment
\end{verbatim}
Isn't it nice?
\end{document}
In order to change the size of the monospaced font, there is a “nasty” trick. Modify the value in the definition of \ttscale to suit your need.
\documentclass{article}
\newcommand{\ttscale}{s*[0.9]}
\DeclareFontFamily{OT1}{cmtt}{\hyphenchar\font -1 }
\DeclareFontShape{OT1}{cmtt}{m}{n}{
<-9> \ttscale cmtt8
<9-10> \ttscale cmtt9
<10-12>\ttscale cmtt10
<12-> \ttscale cmtt12
}{}
\DeclareFontShape{OT1}{cmtt}{m}{it}{
<-> \ttscale cmitt10
}{}
\DeclareFontShape{OT1}{cmtt}{m}{sl}{
<-> \ttscale cmsltt10
}{}
\DeclareFontShape{OT1}{cmtt}{m}{sc}{
<-> \ttscale cmtcsc10
}{}
\DeclareFontShape{OT1}{cmtt}{m}{ui}
{<->ssub*cmtt/m/it}{}
\DeclareFontShape{OT1}{cmtt}{bx}{n}
{<->ssub*cmtt/m/n}{}
\DeclareFontShape{OT1}{cmtt}{bx}{it}
{<->ssub*cmtt/m/it}{}
\DeclareFontShape{OT1}{cmtt}{bx}{ui}
{<->ssub*cmtt/m/it}{}
\begin{document}
ABC \texttt{ABC}
\Large ABC \texttt{ABC}
\end{document}
Compare with the original:
