I'm looking for a way to enforce a 'narrow' math mode in the following sense:
Instead of writing every where the brackets {+} to reduce the spacing like here
\documentclass[10pt,a4paper]{article}
\usepackage{amsmath,tikz}
\begin{document}
\tikz{\node {$d {+} e {=} f$}; }
\end{document}
I'm looking for a way to set a corresponding node property or something similar.

execute at begin nodeis much better, I think. That answer says how to change the spacing for a document but what's needed here as shown below is a way to adapt that so that it only affects the spacing within TikZ nodes. – cfr Apr 14 '16 at 15:00