Yes you can change the title of a hub after it is published.
After several weeks Title Tuner may have some suggestions for words to include in a title, that is available on your "My Account" page.
Or you can go to the hub that you want to change the title of. Click Edit on the menu at the top of the hub.
Click on the Title, you can then change the title to whatever you want.
Bear in mind that as Edgar says you cannot change the URL so some SEO benefits of title changes are not affected, because the Title now no longer matches the URL. Changing the title will help if it clarifies the subject of the hub or introduces better keywords.