Most experts I've heard have warned against changing anything on a well performing video, but then I ask myself... what IS a "good performing" video. A video that is performing "well" but has tags that aren't necessarily ranking, to me theoretically means there's potential for it to rank even better. Just as a good performing thumbnail, could potentially always work even better.
Problem is, changing metadata does reset things for a bit, so you could perform better, or it could halt performance. It's quite the gamble. I have some amazing performing videos with horrible seo from 2015 that I don't dare touch out of fear that they stop performing, but with the addition of chapters, I'm tempted.
That's about all I can say,
@Andrew will definitely have better advice on this one.