is there a way to update or replace a rubric - lets say there's a typo in in - but students have been assessed against it - how can i update or replace the rubric?
Look at the very last paragraph on this page: https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-add-a-rubric-to-a-graded-discussion/ta-...
in particular the last sentence. I am not sure what exactly that means or how it pertains to an assignment rubric. It may mean that you have to regrade the assignments.
I have a way of testing out what you want (without disrupting anything in my course).
I graded an assignment with a rubric for a student. I then went to the assignment and clicked on edit the rubirc. In doing so I get the following message:
So I modified some of the criteria and went back to that student. All the marks for the unchanged entries were still there. However, the entries I changed have to be regraded. so it looks like you can do what you want - you will just have to go back and regrade a few points. By the way you can also add more criteria to the rubric.
A word of warning. I would make sure that the grades are hidden from the students before modifying the rubric. The original grade will show until you regrade and resave the grade with the new criteria.
Hope that helps.