@maya_sonji
Changing the text after marking with it will create a new rubric. Canvas doesn't distinguish between changes made to the comments and changes made to the points.
There is a note below the title of the rubric.
"You've already rated students with this rubric. Any major changes could affect their assessment results."
When I attempt to change a rubric that has been used, it gives me another warning.
"Keep in mind that 2 students have already been assessed using this rubric. Changing it will affect their evaluations."
I went ahead and told it to edit it anyway. Then edited it. I changed the description and added a new rating. I also added a new criterion.
When I reloaded speedgrader, it was using the new rubric, for everyone, but it did remember the previously selected ratings (based on point values). It had no grade for the criterion that I added.
In other words, it seems mostly safe to tweak a few things as long as you're not making major changes.
Canvas doesn't make editing things easy, especially after giving it to students. There are some instructors who might change things the rubric after submissions if it were easier. Canvas thinks rubrics should be public to the student and so if you're publishing rubrics before the assignment is submitted, it's kind of like a promise that you've made to the students. Since Canvas doesn't know if what you changed is altering the meaning, they throw up warnings about it. Canvas would prefer us to have it perfect before we let students see it (I rarely meet that bar myself).
What I have done in the past is I usually catch the mistake very quickly (1 or 2 times through grading). I go through and remove all of the marks from the rubrics for those students I've already graded. Then I fix the rubric and remark it. It seems after my investigation into your question, that it isn't necessary to go to those lengths.
