Switching to different font size(s) locally

Question

Inside a 12pt document I like to switch in an environment to a font size of 10pt. The macros like \normalsize, \large, \small etc. should all work like in a 10pt document. I'm aware that this isn't good typography and might look bad in general. I'm planning to use it for the labels inside a tikzpicture.

The task (I don't like to call it a "problem") is that I have some standalone tikzpicture documents which are using 10pt when compiled standalone, but can be also inserted into 12pt documents where the text does not fit any more in some places. I know it could be fixed by changing all distances to one of the font size specific units em or ex, but don't like to change several figures and maybe add this as a feature to the standalone package.

Answer 1

\let\savednewcommand\newcommand
\let\newcommand\renewcommand
\makeatletter
\input{size10.clo}
\makeatother
\let\newcommand\savednewcommand

Or implement the contents of size10.clo yourself.

Answer 2

\documentclass{article}

\begin{document}
abc {\large abc} 
{\makeatletter\let\newcommand\renewcommand\input{size12.clo}
abc \large abc} 
abc
\end{document}

But it won't work with every class/fontsize. E.g. with book you will have to input book12.clo, and the koma classes computes some fontsizes.