@kbeckford
Not much has changed on this front since the thread in 2015 and classic quizzes are not being developed any more.
If you haven't given the quiz yet, then you can make the extra credit points worth 0 points each. After the quiz has been given, then you can go through and manually grade them to be worth the full points.
If you have already given the quiz, then things become more challenging. You should avoid making changes to a quiz once it's taken.
There are numerous other solutions and hacks available in the Community. You've probably stumbled across those while you were looking for the answer. Here are threads and ideas from the Community just in case you didn't find them and in case someone else coming along wants a list.
This discussion post is outdated and has been archived.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.