@decarbo_michael
Unfortunately, getting more people involved doesn't necessarily increase the likelihood that something will happen. It's partially related to where the comments are. You asked this as a question, which is something that would be deemed to have an answer (even if we don't like it). If you want to suggest a change, then should create a feature idea. That at least gets it into the area where Canvas looks for suggestions.
Unfortunately (we're going to have a lot of unfortunately here) for the person creating the idea, mere suggestion is not enough to guarantee that anything will be done. Canvas has to look at how it fits in with other things and whether it's a big enough problem to spend the resources to fix it. There are a lot of really good ideas (and some not-so-good ones, too), and Canvas doesn't have the resources or desire to implement all of them.
If not a lot of people use freeform criteria with saved rubric comments, it may not be worth the effort to fix. Support for mathematics is extremely limited and you would think there are a lot of people teaching math with Canvas, but little movement has happened there. They would rather a third-party develop something than expend the effort to do it themselves.
Before creating a new idea, though, you should search for existing ideas to see if someone else has thought of this.
When I searched the Canvas Ideas for "saved comments", I came up with [Rubrics] Edit or Delete Saved Comments that was posted six years ago (plus a few days) on February 10, 2019. Since the idea already exists, that's where you would leave your comments.
There are lots of comments people have left and you can see where Canvas has marked it as new and then open different times. That means that they've revisited it over the years and never done anything about it. It's not particularly simple change (to add the interface to editing or deleting the comments), but if they would allow API access to it, then others could write tools or explain how to do it.
I looked into the data and I found where it's coming from. You can get it from the information sent along with SpeedGrader or you can get it from the GraphQL as a rubric assessment on an assignment. But it comes as an array of comments for a particular criterion and none of those have individual IDs. It's part of "summary_data" in the SpeedGrader object, so it may be that they are just stored in JSON somewhere without the ability to edit. But even if we had the ability to replace all of the items through the API, that would be helpful.
Along my research, I did find that if you use the comment library, you can edit and delete those comments. Those are the for the submission comments rather than criteria comments within the rubric.
Personally, I never leave comments within the rubric itself. It used to be too difficult for students to find those, so I started just using the submission comments. Those are still difficult to find, but I make my students go through at the beginning of each class and turn on notifications for them so they hopefully get them in a timely manner. I even inject CSS into my SpeedGrader page to hide the criteria comments so that I have more space and can fit more criteria on the screen at one time.
I realize that doesn't work for everyone and some people like freeform commenting within the rubric.
I don't use the comment library, either, although I often find myself typing the same thing over and over --- sometimes with slightly different wording so that students don't feel like I'm just boiler plating it because they got the same message as their friend did. I do use the multiple clipboard functionality of Windows (I think there are some third party clipboard managers for the Mac). This allows me to repeat things without having to go back and retype them. Some people also create the comments in Word (where they have the benefit of grammar and spell checking) and then copy/paste from there. That's a hassle, so the saved comment feature is useful since it associates it with the criterion. A tip may be to grade a few with copy/paste from a document to make sure you're saying what you want to say before you check the save comment box.
In general, Canvas works best when people do what they should do exactly right the first time. That obviously doesn't happen, so there should be some way to fix mistakes. In most cases there is. This is one example where there isn't a way to fix things. Another thing that cannot be undone is clicking the "Reassign" button.
Some kind of functionality for editing or deleting comments would be beneficial. The best thing to do would be go to that existing feature idea and read through it and add use cases or lend support. This is a feature request posted as a question, so it doesn't have the management tools that feature ideas do and Canvas doesn't even really try to follow ideas presented as questions.
Unfortunately (I told you there were a lot of those here), since it's been out there for six years with no real movement, I wouldn't hold your breath waiting on it to be implemented. That's when we have to look for other ways (like waiting before we hit save comment or moving to submission comments where we can edit and delete them) to make up for lack of features.
