Just note that if YOU send more than X characters, it'll replace your message too!
To avoid this, you should check if the Origin is your name. If it isn't, it should replace it, otherwise it should leave it. However, if you're using StuffPlug 3's chat-only name, this won't work and will also replace your message anyway. And therefore, please check out
CookieRevised's reply to [Fix] Problem with OnEvent_ChatWndRecieveMessage's Origin, where CookieRevised describes how to check if you're using a chat-only name and if necessary, check your chat-only name instead of your actual name.