\reDeclareMathAlphabet{\mathtestA}{\mathrm}{\mathmc}
\reDeclareMathAlphabet{\mathtestB}{\mathrm}{\mathtestb}
\reDeclareMathAlphabet{\mathtestC}{\mathtesta}{\mathmc}
\reDeclareMathAlphabet{\mathtestD}{\mathtesta}{\mathtestb}
\reDeclareMathAlphabet{\mathtestE}{\mathtestE}{\mathmc}
\begin{document}\makeatletter
\reDeclareMathAlphabet{\mathtestA}{\mathrm}{\mathmc}
\reDeclareMathAlphabet{\mathtestB}{\mathrm}{\mathtestb}
\reDeclareMathAlphabet{\mathtestC}{\mathtesta}{\mathmc}
\reDeclareMathAlphabet{\mathtestD}{\mathtesta}{\mathtestb}
\reDeclareMathAlphabet{\mathtestE}{\mathtestE}{\mathmc}
\begin{document}\makeatletter