When you edit questions in a Moodle Quiz, you are actually editing the question in the Moodle Question Bank. Any changes you make will affect any quizzes that include the question, including past quizzes.
If you want to edit a question without affecting other quizzes that include it, you should instead make a copy of the question in the Moodle Question Bank and edit the copy/ Alternatively, you could create a new question.
- Open the question bank in your Moodle course.
Read more on how to access the question bank.
- On the Questions tab, select the category that contains the question you want to duplicate.

- From the Actions drop down menu to the right of the question, select Duplicate.

- Give the new question a name, and make the edits you’d like to the question.Click Save changes.You can now add this edited question to a Moodle quiz.