Here is one that will work on vb4, very simple modification, easy to modify to your own needs. Very few features, but gets the job done. It will not go back through your database and add tags to your old posts. I looked at it years ago so it might have to be upgraded for v4.2.2.
AMP Quick Auto Tagger
https://vborg.vbsupport.ru/showthread.php?t=235469
--------------- Added 30 May 2014 at 16:16 ---------------
Here is another one with more features. Always read the thread and please back up your entire board before experimenting with a new modification.
Thanks @ForceHSS for helping out.
https://vborg.vbsupport.ru/showthrea...ghlight=tagger