Thanks for that!
Badges don't seem to be an option at my institution; the attendance page doesn't have the "roll call" format shown in that link. (This inconsistency is annoying, but that's another issue.)
The situation has become a bit weirder now, because when I went back to look at these excused absences again, the student's overall grade had, in fact, changed, despite Canvas Help having confirmed for me that it doesn't work that way. After a bit of experimenting (which was difficult, because Canvas doesn't provide the "test student" option with attendance - but that's another issue), I found that it takes 5-10 minutes for the grade to update after a change is made in Attendance. (This is also annoying, as you sometimes need to experiment with the factors affecting a student's grade, and it's not practical to wait 10 minutes each time you change something - but that's also another issue.) As it stands, I think the system may be working the way I want. I just wish it were all a bit more self-explanatory; it would be great if hovering over an option told you exactly what it does, instead of leaving you to guess, Google it, have confusing and misleading conversations with Canvas Help, and plead for guidance from the Canvas community. But that's also another issue.