Hi Gina,
I'm sorry but I don't have great answers for you. With announcements there is no real way to post a single announcement to multiple courses.
For Classic quizzes it's also not really possible to change the point value of the Quiz. Classic Quizzes take their total points as the sum of all the points for individual questions. There are re-grading options, but they really are not triggered by changing point values of questions. New Quizzes does let you set the point value of a Quiz independently of the sum of points on the questions. So if you are using New Quizzes that might work for you.
My suggestion would be to create a New Assignment to replace the values for the existing quiz. Set the point value to what you need it to be with your new grading plan and then enter the scaled grades into it. After you've done this I suggest changing the initial quiz into a Practice quiz. This will retain it in Canvas for students to refer to, but will remove it from the gradebook which is what you want since you have a new column to hold those grades.
Rick
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.