BuddyPress.org

I would really be thankful for help on this, I want when users type a message subject, it should include their username at the beginning or end. The Subject should be like this: “Username: Are you coming tomorrow?”
I was reading this useful article: https://samelh.com/blog/2016/01/22/buddypress-how-to-add-custom-content-after-message-text-content/

Thanks in advance!