Is it possible for a candidate who already submitted their response to change it later on?

Yes. The links in the invitation emails do not have an expiration date, so if a respondent wished to change their response they could always click on the link in the email and overwrite the previous response.

Please note: the only exception to this are surveys with a closing date. The closing date feature is available for Employee Engagement accounts. Check out our FAQ article on adding a closing date to your survey here.

If you want to avoid this as much as possible, you can enable a setting that will show your respondent the last scores they have given: this way, if they happen to forget they have already submitted your survey, they will immediately be reminded of that! Learn how to enable this settings in your Advanced survey settings.