Be careful about what your syllabus says and how you are going to explain the change to your students.
If the syllabus says something like 900 points = A, 800 points = B, etc., then that's a potential problem if you change the denominator. Because students who have earned a given number of points will believe they have already earned the corresponding grade in the syllabus.
However, if the syllabus says 90 percent = A, 80% = B, then you'll have an easier time of it.
Still, I'd be worried that a student who has been tracking his or her grade total so far and comparing it to the original "Total Possible" has been misinformed all semester about how many points it takes to earn a given grade.
I think it all depends on how much your syllabus emphasizes percentage of total rather than sum of total points.
I totally see posters' points about the number of points for a certain grade. My syllabus states X points for exams, X points for quizzes, X points for homework, etc, to the total. But then states that 90% is an A, 80% is a B, etc.
The reason I don't drop quiz grades is b/c they are all worth a different number of points. If the chapter is long, the corresponding quiz will cover more material and therefore be worth more points. If the chapter is short, then I write a shorter quiz, worth fewer points.
Thanks for giving me more angles to think about!