If you don't want to show a core, or contrib message to the end user, you now have to iterate $_SESSION['messages']
and search for the (translated, token replaced) string to unset it.
If a message has a unique key, you can easily override a message, or unset it.
function backdrop_set_message($message = NULL, $type = 'status', $repeat = TRUE, $message_key = FALSE) {
A simple unset($_SESSION['messages']['status']['unique_key'])
could remove the message, and $_SESSION['messages']['status']['unique_key'] = t('Something else');
changes it.
Recent comments
What about Ubercart, Rules and Membership Entity? (theoretically, haven't tried it myself)
Suggest for - Backdrop Commerce
Just edit .htaccess in /files folder remove "-ExecCGI -Includes" in string "Options -Indexes -ExecCGI -Includes"
CSS and JS aggregation not working
This comment has been removed by myself.
Suggest for - Backdrop Commerce