Select video clip and holding shift select also the audio track below (they should be the same lenght for better result). Then right click on selection an press on link option.
but does linking actually over-write the original track creating one with the new audio
it doesnt seem to
You can always just put it on its own sequence and then use the sequence as a clip.
Especially now that the sequences can be scrubbed in the Project panel using the latest version CC.
That method allows you to go back and edit the sequence, change it around, whatever.
No it won't but you can always render just that clip with the new audio track. If you do it will of course compress your video more then. I think it is better just to link the audio and let it go this way. It's up to you then