I have a text file which has a particular line something like
sometext sometext sometext TEXT_TO_BE_REPLACED sometext sometext sometext
This line is removed by the admin.
You can use the change command to replace the entire line, and the -i flag to make the changes in-place. For example, using GNU sed:
sed -i '/TEXT_TO_BE_REPLACED/c\This line is removed by the admin.' /tmp/foo