🚀 go-pugleaf

Michael DeCorte's first advice is right: Shoot the guy who made those rules.
(Michael formulated it more politely).

Michael's second advice, namely copying a piece of code from art12.sty and
modifying it, is relatively simple and has only one drawback:
It doesn't work.
(At least when I just tried it. Rule #1 for TeXhackers: Never believe that a
macro works until you preview the result)

The following worked for me:

Like Michael, I assume that you are using a 12pt style. I further assume that
you use \normalsize formulas (This is the default and is one of the  reasons why
Michael's rules don't work: His changed definition of \scriptsize will normally
never be executed.) The \normalsize command (which you don't normally see, it is
executed by the \begin{document} command) in a 12pt style uses the command
\xiipt to set the various fontsizes. The command \xiipt is defined in the file
lfonts.tex, and this definition has to be changed.

To use the changed definition, you can
1. put it into a dumb.sty file and use
\documentstyle[12pt,dumb]{article}
as Michael suggested, or you can
2. put it into your .tex file. In that case, you have to enclose it between
\makeatletter and \makeatother (to make the @-signs work). Make sure that the
new definition appears (after the \documentstyle statement and) BEFORE the
\begin{document} statement (then it is valid throughout your document), or else
you have to activate it by inserting a line
\@normalsize \normalsize
right before the \makeatother statement. (Try it, it won't work otherwise!) In
this way, you could switch between different styles inside your document.

The changed definition follows (I have changed all cases of six, sev, egt, or
nin to ten)
%
\def\xiipt{\textfont\z@\twlrm
  \scriptfont\z@\tenrm \scriptscriptfont\z@\tenrm  % <--
\textfont\@ne\twlmi \scriptfont\@ne\tenmi \scriptscriptfont\@ne\tenmi  % <--
\textfont\tw@\twlsy \scriptfont\tw@\tensy \scriptscriptfont\tw@\tensy  % <--
\textfont\thr@@\tenex \scriptfont\thr@@\tenex \scriptscriptfont\thr@@\tenex
\def\unboldmath{\everymath{}\everydisplay{}\@nomath\unboldmath
          \textfont\@ne\twlmi
          \textfont\tw@\twlsy \textfont\lyfam\twlly
          \@boldfalse}\@boldfalse
\def\boldmath{\@ifundefined{twlmib}{\global\font\twlmib\@mbi\@magsc
ale1\global
        \font\twlsyb\@mbsy \@magscale1\global\font
         \twllyb\@lasyb\@magscale1\relax\@addfontinfo\@xiipt
              {\def\boldmath{\everymath
                {\mit}\everydisplay{\mit}\@prtct\@nomathbold
                \textfont\@ne\twlmib \textfont\tw@\twlsyb
                \textfont\lyfam\twllyb\@prtct\@boldtrue}}}{}\@xiipt\
boldmath}%
\def\prm{\fam\z@\twlrm}%
\def\pit{\fam\itfam\twlit}\textfont\itfam\twlit \scriptfont\itfam\tenit  % <--
   \scriptscriptfont\itfam\tenit % <--
\def\psl{\fam\slfam\twlsl}\textfont\slfam\twlsl
     \scriptfont\slfam\tensl \scriptscriptfont\slfam\tensl % <--
\def\pbf{\fam\bffam\twlbf}\textfont\bffam\twlbf
   \scriptfont\bffam\tenbf \scriptscriptfont\bffam\tenbf
\def\ptt{\fam\ttfam\twltt}\textfont\ttfam\twltt
   \scriptfont\ttfam\tentt \scriptscriptfont\ttfam\tentt
\def\psf{\fam\sffam\twlsf}\textfont\sffam\twlsf
    \scriptfont\sffam\tensf \scriptscriptfont\sffam\tensf
\def\psc{\@getfont\psc\scfam\@xiipt{\@mcsc\@magscale1}}%
\def\ly{\fam\lyfam\twlly}\textfont\lyfam\twlly
   \scriptfont\lyfam\tenly \scriptscriptfont\lyfam\tenly % <--
 \@setstrut \rm}
%

--Martin Costabel