[Georgio]

Код:

@echo off& :команда "echo off" обязательна
set "word_1=the"
set "word_2=мама"
(
for /f "usebackq delims=" %%i in ("1.txt") do (
 for %%j in (%%i) do (
  if /i "%%j"=="%word_1%" (
   set /p"=%word_2% "<nul
   ) else (
   set /p"=%%j "<nul
   )
  )
  echo.
 )
)>"2.txt"
move "2.txt" "1.txt">nul
exit /b