If you give tab space to specific file with append a word or lines using shell command,

​#  echo -e ' \t '
 
echo a tab space newline

If you give tab spece to specific file with append a word or lines,
 
#  sed -i "/find word/a\t append word" file_name.txt

or multiple tab,
#  sed -i "/find word/a\t\t\t append word" file_name.txt