To avoid blank line skipping (give readability in conf file) I combine aflat and jeb answer (here) to something like this:
@echo off
setlocal enabledelayedexpansion
set INTEXTFILE=test.txt
set OUTTEXTFILE=test_out.txt
set SEARCHTEXT=bath
set REPLACETEXT=hello
set OUTPUTLINE=
for /f "tokens=1,* delims=¶" %%A in ( '"findstr /n ^^ %INTEXTFILE%"') do (
SET string=%%A
for /f "delims=: tokens=1,*" %%a in ("!string!") do set "string=%%b"
if "!string!" == "" (
echo.>>%OUTTEXTFILE%
) else (
SET modified=!string:%SEARCHTEXT%=%REPLACETEXT%!
echo !modified! >> %OUTTEXTFILE%
)
)
del %INTEXTFILE%
rename %OUTTEXTFILE% %INTEXTFILE%