Is it possible that "built-in" means that it's using the default set, and to customize it you are meant to replace "built-in" with the name of a file?
ETA: OK, it looks like to change it you can put this in the my.ini file:
Code:
[mysqld]
ft_stopword_file=""
(or put a file name in the quotes if you want to provide an alternate list of words).
I haven't tried to see how it affects searches but it changes what is reported as the value of that variable. I guess the next question is how you go about rebuilding the indexes.
ETA: I tried it on my Windows system at home, maybe it's different on a Linux server.