@akoticha
In Classic/Legacy/Old Quizzes, you can edit the HTML on the page after generating the values. It is an unsupported hack I found, but it works because Canvas generates the responses in the browser and then sends them to the server rather than having the server generate them. See https://community.canvaslms.com/people/james for all of the details.
There is no way to automatically delete duplicates, although just a few days ago I was thinking that would be a really cool thing to have. If I wanted 20, I might generate 50 and then remove the duplicates (it all depends on the number of allowable solutions).
You cannot delete some responses and then generate additional ones, the Generate button wipes out any existing solutions.
In the hack I linked to, I have not attempted to delete rows completely to see what would happen. If you attempt this, please leave a comment on the page about how it works. I have a suspicion that it would work just fine, I just haven't tested it to make sure.
We are not using New Quizzes and I have not explored what is possible there, yet.
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