Yes you can tie new audio to old video, but it’s somewhat dependent on the format. I think the easier is if you are working of a video that comes in a MKV which is basically a package, there are tools that allow to add stuff to the MKV (more subtitles and more audio tracks, most of the time).

If you think it’s too big a hassle, wait until you hear about what happens if there’s a second of difference in the timing of the original and your new audio…

I don’t know of any trivial way to do this, maybe some kind of VLC function?