I’m involved in the production of a site and I found the need to disable WordPress’s detection of duplicate comments. While often a good idea there are times in certain use-cases to turn it off. In my case the comments system was being used to communicate back and forth with individuals over the content of a custom post type. More of a case of order processing. It worked out nicely. However it was common for us to repeat ourselves, even within the same conversation.
The only solutions I found were either editing a core WP file.(NEVER EDIT WORDPRESS CORE! Every time you do a kitten dies.) There is another solution.. several years old, that temporarily wraps the comment content in a random md5 hash. Nice trick, but that filter ends up going out in email alerts about the comment. The proper way to do it is to remove the filter that does the duplicate detection! Filters are important to understanding many of the things that happen to content like wrapping chunks of text in p tags and processing shortcodes.
Here is what I added to my theme functions.php file:
A single line in your functions.php file. Nice, eh?