I just found out that there are two (or three?) more places where the new NoEmail & SpecialNotice assignment needs to also reset the FO settings, as they still allow you to "set" your subscription to either NoEmail or SpecialNotice while keeping the FO settings you had before.
A. If one has a group set to Indiv/digests/summary + FO(...), the "Your Groups" page (groups.io/groups) allows you to select one or more groups and set them to either NoEmail or SpecialNotice, and it will do so but it also keeps the previously-selected FO settings.
B. Same in the Unsubscribe page (from email message link, ../<groupname>/leave/.../.../.../xyzzy) or Sub settings page -> Leave group -> "Verify Leave" dialog, it gives you the option to "Switch to Special Notices", which also resets you to Special Notices but it also keeps the FO settings you had before.