[Alexander_88]

Вот получилось вроде

Код:

@echo off
 
set "C:\Users\Alexander\work\new script test"
set "mask=*.jpg"
set "suffix=_m"
 
pushd "%dir%"&& (
for /f "delims=" %%i in ('2^>nul dir/a-d/b "%mask%"') do ren "%%i" "%%~ni%suffix%%%~xi"
popd
)