Hello @robin-cruise and All,
Why not this S/R :
SEARCH (?-s)^\h*<div class="fb-comments" data-href=".+
REPLACE <!-- Facebook Comments $0 -->
Notes :
This regex would search all contents of any line, beginning with the string <div class="fb-comments" data-href=, possibly predeced with any leading horizontal blank chars, and places this line in comments, with the syntax <!-- Facebook Comments ............... -->
Not a very difficult regex : you could have found out this one, by yourself ;-))
Best Regards,
guy038