I just had and solved a similar problem of my own. The problem in my case is that the my.ini file I needed to edit in order to change the ft_min_word_len variable was in a directory that's hidden/protected by default in Windows 7. That's: "c:/programdata/mysql/mysql server 5.7".
Windows file explorer and searches don't show this location until you go into folder options and specify that you want to see hidden files/folders (and possibly protected operating system files--I did both).
Initially I created a my.cnf file under Program Files/MySQL Server 5.7. But when I restarted the server the ft_min_word_len variable hadn't changed. Then I typed in some random text that I knew should trigger an error, but the server started up like normal. It seems that MySQL wasn't reading the file, even though it was in one of the locations specified in the help text from the MySQL client shell.
My thinking is that the MySQL server starts searching for .cnf/.ini files in the order specified in the help text, but once it finds a valid file, stops searching. Just a theory, but I can say for sure that it wasn't recognizing configuration files in the other places it was supposed to be looking.
I figured it was like CSS, where each new CSS file overrides settings in the previous. Evidently not.
Anyway, I hope this will be of help to anyone else who runs into the same problem.