There does not seem to be an "Un-Split Audio" feature.
What do I mean by that?
Well, there is a command "Split Audio" which splits a clip with audio+video into separate video and audio tracks. Once done, there does not seem to be a way to later on undo that splitting. Am I right or did I overlook something?
If I am right (please give me some feedback on this) I should file a feature request accordingly.
Kind regards.

I am editing theatre-footage, which was filmed with three separate cameras and thus I have three different audio-tracks ready to use. What I did was to basically stay with one distinct audio-track and delete the other two. Now I find that here and there my selected audio track is not as good as it might be with the other audio tracks. So for certain clip-parts, I would like to get the audio back by just "Video-Audio-Un-Splitting" the Video-Track-Part, which I can see on the timeline, which does not hold the Audio anymore. Unfortunately this - in theory very simple task - does not seem to be possible at the moment with kdenlive.