[OS X TeX] \newcommand problem with sn-jnl.cls

[Roussanka Loukanova]

Dear All,

I have a question that is off the list, but I hope to get it resolved
with your help.

I have to use Springer's style for journals  <sn-jnl.cls> from the
Springer package:
sn-article-template
downloadable at:
https://www.springernature.com/gp/authors/campaigns/latex-author-support#c17590862

I have my own style file of defined \newcommand{...}{...} and
\DeclareMathOperator{...}{...}.

Typesetting (by pdflatex) .tex files that use Springer's cluster
\documentclass[sn-mathphys]{sn-jnl}
produces errors adding my own definitions in .tex files, by:
 \usepackage{exadefs} / or /imput{exdefs.sty}

I get the error even if I add a single definition
\newcommand{\R}{\mathbb{R}}
in the preamble of Springer's  template file  <sn-article.tex>.
 I get the following error:

==
ERROR: LaTeX Error: Command \R already defined.

--- TeX said ---
               Or name \end... illegal, see p.192 of the manual.
==

I would appreciate help.

Best Regards,
Roussanka