If your change is limited to adding new logic, but not deleting or modifying any existing questions, then it will not affect data that has already been collected. Just make sure to publish the change once you have tested it so it goes live!

Any changes made to the survey won’t affect anyone who are alrady taking or in the survey. Only the respondents new to the survey will be affected. And yes, if you delete the questions, the consequent data will also be deleted so beware! just a headsup!

Adding and removing branch logic, display logic, and skip logic does not delete previously gathered survey data. All you have to do is to Publish the survey again. Publishing a survey only affects new respondents. Responses in progress will be unaffected.