MySQL :: 16 Characters Limitation About A Username Length

I am unable to create a user in mysql with 20 characters length. I am getting the annoying error message about 16 characters limitation about a username length. I have tried to increase the character user limit length to 32 characters using the following commands:

mysql -uroot -p

use mysql;

alter table `user` modify `User` CHAR(32);

FLUSH PRIVILEGES;

quit

service mysqld restart

But after all of this was done I was and I am still unable to connect to mysql anymore with/without password.