Enabling Mirrored MIDI Editing
To enable Mirrored MIDI Editing, do one of the following:

Select
Options > Mirror MIDI Editing.

Enable the Mirrored MIDI Editing button in the Edit window, MIDI Editor window, or Score Editor window.
Mirrored MIDI Edit button in the Edit window
In Mirrored MIDI Editing mode, the Mirrored MIDI Editing button flashes Red once as an edit is made to alert you that your edit is being applied to more than one clip.