Can YouTube video titles be changed / updated?

The short answer is yes (but be mindful of your changes). In YouTube Studio you can click edit next to any previous video and update the video title.

When you do this (in fact if you change any video data including descriptions, tags or hashtags) YouTube re-evaluates your video and may update its position in search results depending on a mixture of the changes you’ve made and the previous watch time data achieved.

This can be good or bad: if you had a video that wasn't very optimized and wasn't getting a lot of searches, updating the video title could indeed help push it out further. However, if you have a video that was getting consistent views, changing the title (or any other metadata) could disturb that.

Once a video has achieved some views, the watch time / audience retention becomes a strong signal, so if you have videos with poor retention, any amount of optimizing you do around the video title won’t likely lead to significantly improved performance in the future.