There may be a langauge/translation issue here, as it's not clear to me what you mean by a "broadcast message", but if you are concerned aout new posts showing up in the middle of an existing thread, that happens when the person making the post clicks the reply button in the middle of the thread - he (or she) can choose where they want to reply.
Broadcast messages?
There may be a langauge/translation issue here, as it's not clear to me what you mean by a "broadcast message", but if you are concerned aout new posts showing up in the middle of an existing thread, that happens when the person making the post clicks the reply button in the middle of the thread - he (or she) can choose where they want to reply.