I was looking in the menus of Ableton Live 9 and noticed that there is a keyboard shortcut for Deactivate Clip(s). Highlight a clip and hit the numeric number 0 and it becomes deactivated. Was this there in previous versions of Live? Now let’s get Ninja status ok? Highlight a MIDI note and hit the numeric 0. See that? It works there too! It’s incredibly useful so commit that to memory. Happy music making.
“To deactivate, or mute, a note (or notes) in the MIDI Editor, select it and press . The Deacti- vate Note(s) command will mute the note, making it appear gray in the display. Press  again to reactivate notes. You can de- or reactivate all of the notes in a single key track at once by clicking a key on the piano roll and pressing .” – Ableton
For more info: ableton.com