Hi @mbruce . I haven't run into the need to do this myself, but came across this thread the other day on the topic so I thought I would pass it along in case it is helpful.
The thread was created a few years go, so maybe someone knows of an update that expands your options.
@mbruce , our institution's instructors regularly use the "Assign Grades to Each Student Individually" option (available in Assignments with "This is a Group Assignment" checked) when one or more group members' grades need to differ from the grade generally earned by that group. The setting is discussed in the thread ericwerth linked and @kona mentioned.
The best time to check the "Assign Grades to Each Student Individually" option is usually after you've entered the grade most group members will earn. Earlier this year, I discussed using this in a CanvasLIVE event, GROUPIES: Group Assignments.
After entering the group grades, you can edit the assignment and uncheck "group assignment." Then you can go to your grade book and change individual grades.
I did exactly what David Geiger suggested after I found I had assigned group grades and realized a student was absent on the date the assignment was completed in class and deserved a zero. I went to the assignment and selected edit and then went and unchecked the group assignment box and saved.
Hello there, @mbruce ...
I have been reviewing older questions here in the Canvas Community, and I came across your question. I wanted to check in with you because I noticed that we have not heard back from you since you first posted your question on December 12, 2017. It looks as though you have received some good feedback from various members of the Community including ericwerth, @kona , @RobDitto , @geiger , and @dshively . Did any of their responses ultimately help to answer your question? Or, are you still looking for some help with your original question? If you feel that one of the above responses has helped to answer your question, please go ahead and mark that one as "Correct". However, if you are still looking for some assistance from members of the Community, please come back to this thread to provide an update so that someone might be able to assist you. For now, I am going to mark your question as "Assumed Answered" because we've not heard back from you and because there hasn't been any new activity in this topic since mid-December 2017. However, that won't prevent you or others from posting additional questions and/or comments below that are related to this topic. I hope that's aright with you, Michelle. Looking forward to hearing back from you soon.