Tim might be able to jump in and give more advice.
First, what I would do is to go to the question bank, edit the question there and replace the word. This kind of edit I think should work for most question types. Any student who has not started the quiz will see the question with the new word.
Somehow, I recall giving exams and in the middle of the exam being able to change the answer. But I cannot recall if this depends upon they type of question being use. When I do this, I can also go into the quizzes that have been attempted and do a regrade. It's been a really powerful feature. I can't tell you which versions of moodle I was using when I did this.
Some experimenting for better understanding might be helpful.