You can cut/copy/paste/paste in place selected Keyframes between Tracks, even between different Compositions. Pasting can be occurs in the playhead position, or at the original time of the Keyframe(s) if you use Paste in Place. Keyframes values will be converted to be compatible with the destination Tracks minimum and maximum values settings.
Update a Keyframe
When you paste one Keyframe to a location where an other Keyframe already exists and that Keyframe is selected, the new one will replace the old one, instead of creating a new.