[Tex/LaTex] Upright Lowercase $\pi$ as Default

Question

This question has helped me in creating a command for my own package (more a list of commands I defined) to force upright lowercase \pi, and so in my package I have the following code:
\renewcommand{\pi}{\text{$\mathup{π}$}}

I don't want to include my entire package here because it's huge. So, as a simpler example, when I run the following code (in LuaLaTeX) it works fine and the pi becomes upright:

\documentclass{article}
\usepackage{unicode-math}
\usepackage{amsmath}
\setmathfont{xits-math.otf}    %I use MinionMath-Regular.otf but should work the same
\begin{document}

 \renewcommand{\pi}{\text{$\mathup{π}$}}
 \verb|\pi| = \pi $\pi$       
 %I put both \pi and $\pi$ here just to show that it can work in and out of math mode.

\end{document}

But, it only shows pi as uppercase this for that particular line! If I go to another place in the document and try $\pi$, it reverts to italicised! Since I'd rather not have to type in $\mathup{\pi}$ or $\mathrm{\pi}$ each time, is there any way to force this command as a default instead?

Below is a screenshot of what I would like as default (left) and what I wish to avoid (right):

Answer 1

I would follow egreg's comment, all italic, or all upright. In case it's a special occasion, then don't redefine \pi but define another command.

\documentclass{scrartcl}
\usepackage{mathtools}
\usepackage{unicode-math}
\setmainfont{Minion Pro}
\setmonofont{Consolas}[Scale=MatchLowercase]
\setmathfont[Scale=MatchLowercase]{TGPagellaMath}
\AtBeginDocument{\renewcommand*\pi{\mathup{π}}}
\begin{document}
\begin{tabular}{rl}
  \verb|\pi|:            & $\pi$                 \\
  \verb|π|:              & $π$                   \\
  \verb|π| in text mode: & π \emph{π} \textbf{π} \\
\end{tabular}
\end{document}