You arent supposed to add lines.
Only replace a module on the line if you happen to have a deprecated one.
(the post in unstable wasnt very explanatory because … well … its in Unstable.)
Handling pacnews or deprecated configuration is all a bit nuanced … there isnt a single rule and its all system-dependent.
As seen here:
https://wiki.manjaro.org/index.php?title=Pacnew_and_Pacsave_Files#Managing_pacnew_and_pacsave_files
and here:
Good tutorial around pacnew needed