@akulikow -
I understand your frustration. As a way to possibly make the process a little less painful, I will offer the following method which may work for you (I don't know because you did not fully explain the setup you are using).
I will assume that you are using a points based gradebook. Also, the quiz score total is incorrect and you are willing to just add or subtract the same number of points to each quiz. In this case, just create an assignment with the name of Quiz X adjustment - you can put information on the assignment as to what the adjustment is and why you are doing it. Make the assignment worth 0 points. Then in the gradebook, go to that assignment and select the default grade option from the ellipses menu for the assignment. make the default grade whatever you want - i.e 2 (for adding 2 points) or -2 for subtracting 2 points.
If you are using weighted assignment groups, then the same approach works there, it is just that the assignment needs to be in that group.
Let me know if that helps.
Ron