- The menu option "Turn Google Music Access on" should read "Off" when you want to disconnect from google music
It is undocumented feature

Supposed that you disconnect from Google by right-clicking Google 'device' and selecting 'Safely Remove'
- I tried to delete some tracks using the plugin with no success. I proceeded to delete them using Google Music directly but the changes didn't reflect in the plugin even after refreshing. I had to log out and login in again to see the changes.
Deleting tracks from plugin (and manual adding to Google Play eg. by drag-n-drop) can be done if somebody needs this.
Reflecting deletion by refreshing also can be done. Its known issue, but thought nobody encounters this issue.