documentclass[]{article}
usepackage{amsmath,amsthm}
%done by macro1.tex
theoremstyle{definition}
newtheorem{thm}{Theorem}[section]
%done by macro2.tex
theoremstyle{plain}
makeatletter
letthmrelax
letc@thmrelax
makeatletter
newtheorem{thm}{Theorem}[section]

usepackage{kantlipsum}
begin{document}
begin{thm}
kant[1]
end{thm}
 end{document}