You're correct that if you select an option as the default answer, anywhere that field is used will carry that same default, the same behavior about any other properties of the field.
Have you looked into adding validation language to the field? Validation was something released earlier this year, see more about it here towards the bottom of the article. It won't automatically fill in an answer but it could help guide the user on what to fill in based on answers to other questions.
If this helped you, please mark correct to help others : )