The problem that I can see with those scripts is that if the person is changing nicks several times per second, then by the time your mIRC sees it and reacts, their nick has already changed. It may be that the server will automatically redirect the kick to their new nickname, but that's not guaranteed.

Some servers provide a mode (+N on my server) to prevent users from changing nicks in your channel. You could set that mode in your channel permanently, or a few lines could be added to one of the above scripts. If the script sees someone nick flooding, ban the user, set +N in the channel, wait a second or two, and then kick the user out.