[Starter1]

@echo off
setlocal enabledelayedexpansion
Set infile=1.txt
Set find=###
Set replace=Автор Петрович.
@echo off
setlocal enabledelayedexpansion
set COUNT=0
for /F "tokens=* delims=," %%n in (!infile!) do (
set LINE=%%n
set TMPR=!LINE:%find%=%replace%!
Echo !TMPR!>>TMP.TXT
)
move TMP.TXT %infile%le%