<i>But other BBs give possibilities to edit members' nicknames </i>
Other BBs giving a lot of another possibilities... what we are talking here is already <b>your</b> freedom - to choose something you like more. miniBB is our board, with our concepts and vision, so... you know.
It is possible to change nicknames only manually executing SQL requests. Knowing user's ID
(integer), you can execute the following commands, for example:
update minibbtable_users set username='NEW_USERNAME' where user_id=USER_ID;
update minibbtable_users set topic_poster_name='NEW_USERNAME' where topic_poster=USER_ID;
update minibbtable_users set poster_name='NEW_USERNAME' where poster_id=USER_ID;