Audio/Video editor for macOS
If lightweight means command line, then get ffmpeg


https://brew.sh - install homebrew package manager
brew install ffmpeg
profit


See any of the plethora of tutorials online or questions on the network :


https://stackoverflow.com/questions/9446578/how-to-replace-audio-track-in-mkv-file-on-ubuntu-11-10
https://superuser.com/questions/800234/how-to-replace-an-audio-stream-in-a-video-file-with-multiple-audio-streams
https://stackoverflow.com/questions/11779490/how-to-add-a-new-audio-not-mixing-into-a-video-using-ffmpeg