Allow other modules to change submission message

What's an example message you are wanting to override this to? Seems a bit overkill for a message to have an alter behavior to it. Would https://www.drupal.org/project/stringoverrides make more sense to globally override the message?

you can still target like:

%type (%id) has been replicated to id %new!

and then use the same tokens in the new message:

Replicated %type: %new

Are you bringing along other data? I'm not really against adding it this just seems overkill for 1 message to be posted.

Ok that makes more sense. Could it make more sense to have the message able to be disabled as a setting? Then you could use normal form_alter hooks or hook_replicate_entity_alter (from replicate module) to fire off your message you are looking for.

or jumping in on hook_replicate_entity_alter directly and then you have full access to any entity right after replication and can also make it specific to type if needed

The alter is called after it's been cloned and contains the clone as well as the original

hook_replicate_entity_alter

function replicate_clone_entity($entity_type, $entity) {
  $clone = clone $entity;

  if ($clone) {
    // Let other modules manage the cleaning of the entity.
    foreach (module_implements('replicate_entity_' . $entity_type) as $module) {
      $function = $module . '_replicate_entity_' . $entity_type;
      $function($clone);
    }

    // Set the entity as new entity.
    $clone->is_new = TRUE;

    // Let other modules do special actions on each field.
    replicate_clone_fields($clone, $entity_type);

    // Let other modules do special actions on the global entity.
    drupal_alter('replicate_entity', $clone, $entity_type, $entity);
  }

  return $clone;
}

Your proposed patch would provide a solution I like more where you could just set that flag and then it hides the message. hide_message could conflict w/ the rest of the universe of projects so maybe like replicate_ui_hide_message

Drupal 7 is EOL.