Although a questionnaire is in the field, you could modify it.
But you have to be aware of the following issues:
• In general, questionnaire texts could be modified. But you have to ensure that you do not modify the text in a way that a question or an item looses its meaning.
• If you delete a question, all data which is linked to this question will be deleted as well.
• Ex post changes of the structure of a questionnaire are also possible.