You can expect improvements in click-through rates, viewer engagement, and potentially rediscovery by a new audience.
It's just like you've re-uploaded the video... But without doing it!
Realistically, your video can only go up in ranking. Nothing can go wrong — worst case worst, you would've never updated the video, right?
Positive changes in engagement and click-through rates can indeed improve a video's ranking and visibility on YouTube.
Yes, absolutely! If you're not satisfied with the test results, you can easily revert to the original thumbnail and title.