Rileggendo mi sono reso conto che difficilmente mi potrete aiutare senza uno stralcio di codice per pacchetto chemmacros
`
…
\RequirePackage{mathtools,environ}
\newtagform{CMreaction}{(}{)}
\newcounter{save@reaction}%
\newcounter{reaction}%
\newcommand*\CM@AtBeginReaction{\setcounter{save@reaction}{\value{equation}}\setcounter{equation}{\value{reaction}}\usetagform{CMreaction}}%
\newcommand*\CM@AtEndReaction{\setcounter{reaction}{\value{equation}}\setcounter{equation}{\value{save@reaction}}\usetagform{default}}%
% \newreaction*+{
% * and + are optional
\NewDocumentCommand\newreaction{st+mm}{%
\@ifundefined{#3}{%
\IfBooleanTF{#2}{%
\NewEnviron{#3}[1]{\CM@AtBeginReaction\begin{#4}{##1}\expandafter\cee\expandafter{\BODY}\end{#4}\CM@AtEndReaction}
\IfBooleanTF{#1}{%
\NewEnviron{#3*}[1]{\begin{#4*}{##1}\expandafter\cee\expandafter{\BODY}\end{#4*}}%
}{}%
}{%
\NewEnviron{#3}{\CM@AtBeginReaction\begin{#4}\expandafter\cee\expandafter{\BODY}\end{#4}\CM@AtEndReaction}
\IfBooleanTF{#1}{%
\NewEnviron{#3*}{\begin{#4*}\expandafter\cee\expandafter{\BODY}\end{#4*}}%
}{}%
}%
}{\PackageError{chemmacros}{The environment/command #3 is already defined}{}}%
}
…
`
Mi aiutereste a ridefinire il tag?