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This plugin adds Theme menus in the admin bar. 
You can switch and activate the theme on the admin bar. 
You don’t need to go to the administration screens to switch the theme.
(For Japanese User) 管理バーにテーマメニューを追加します。 管理バー上でサイトテーマの変更・有効化が行えます。 テーマを変更するために管理画面に行く? 要がなくなります。

Switch theme on admin bar

This plugin adds Theme menus in the admin bar. You can switch and activate the theme on the admin bar.

Michael Dance

This humble plugin adds an option in Settings > General that controls who sees the WP Toolbar when viewing your site.
You can turn the Toolbar on or off per user role.
Note that this controls the public, front-end version of your site. When viewing the dashboard, the toolbar always appears.
How is this different from other plugins that do similar things? It’s smaller, cleaner, and doesn’t add any unnecesary settings pages. It’s also smart enough to hide the Toolbar option on user profiles if that user is already restricted from seeing the toolbar.

Disable Toolbar

Control who sees the WP Toolbar when viewing your site.

Switch theme on admin bar vs Disable Toolbar