Hi gt1020,
Once shortcode is created, the “shortcode name” cannot be edited by default always. It is not a behavior change in 4.1.8
The reason is, once shortcode is created, most people will insert them into posts and pages. Later if the shortcode name is changed, then all the shortcodes in all the pages have to be edited.
To avoid this shortcode name cannot be edited.
To go forward in your case, you can create a new shortcode with the new name and copy paste the old shortcode content and delete the old one.
This way is preferred because people are aware that the old shortcode won’t work and new one has to be replaced in all the posts and pages.