Re: change my.ini at run time

[Rick James]

Unfortunately, a change to ft_min_word_len requires a restart of the server, and cannot be changed dynamically.
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html

If you modify full-text variables that affect indexing (ft_min_word_len, ft_max_word_len, or ft_stopword_file), or if you change the stopword file itself, you must rebuild your FULLTEXT indexes after making the changes and restarting the server. To rebuild the indexes in this case, it is sufficient to do a QUICK repair operation:

mysql> REPAIR TABLE tbl_name QUICK;

Alternatively, use ALTER TABLE with the DROP INDEX and ADD INDEX options to drop and re-create each FULLTEXT index. In some cases, this may be faster than a repair operation.