Is it possible to change the background automatically when charging battery? This is a feature of older nokias, I would like to have it on android! On a related note, it would be nice to have a different background when silenced or on airplane mode.
Yes, using Tasker.

See "Set Wallpaper" action and "Power" state. It even looks like it'd be rather easy to configure that event.

For your related notes, also see "Airplane Mode" state and %SILENT variable.