Yes, you can modify the registration form at any time, add new questions, and modify existing questions. 

WARNING: If you delete a question, all associated answers will be deleted as well. If you change the answers to a question and participants have already answered it, it may cause those values to change as well and skew your results.  You can send an email with a link to update the registration information to your already registered participants.

If you are using the ConnexMe mobile app, participants can also change their registration information from the app.