This Plugin replaces the get_avatar function in pluggable.php to pass an alternate image to gravatar.com that generates the user’s display_name if they do not yet have a gravatar.
More features coming soon…
Plugin Updated Nov-17th

Display Name If No Gravatar

This Plugin passes an alternate image to gravatar.com that generates the user's display_name if they do not yet have a gravatar.

Benoti

Brozzme Change Username is a one click tool to modify any user username everywhere.
To apply a new name, you just need to to select an user and put its new username. 
This plugin will detet any user_login with an “admin” sequence. It will secure your WordPress from bots that will try to access to your WordPress back-office. 
This plugin doesn’t have any options settings.
Link to <a href="https://brozzme.com/" title="Brozzme" rel="nofollow ugc">Brozzme</a> and <a href="https://www.wpserveur.net/?refwps=221" title="WPServeur WordPress Hosting" rel="nofollow ugc">WPServeur</a>.

Brozzme Change Username

Easily change a WordPress Username, save time, increase security.

Display Name If No Gravatar vs Brozzme Change Username