____This modification seems to be better, and a lot more full featured than this one:
https://vborg.vbsupport.ru/showthread.php?t=165951
____However, it does do one thing that yours doesn't appear to do, or allow for. When a new user registers, can you add an option in the ACP where the thread will appear to have been written by that very user (the one who just registered)? If you added that, then that would make this modification nearly perfect for it's purpose.
____Another idea that builds on this, if it's not too hard to implement, would be to have the user automatically subscribe to this new Introduction thread. Again, this would be an option within the ACP. If you added this as well, then this modification would indeed be perfect for it's purpose.