Can I edit or add more questions to a survey block, once a survey is in progress?

Hi - I'm hoping to hear from anyone who has successfully edited or created a new survey block once a survey has begun collecting responses. Some background: I'll be deploying a survey with three question blocks, and I will be creating two different contact lists for this survey with embedded data. The embedded data for contact list 'A' will trigger display logic that will let them see blocks 1 & 2. The embedded data for contact list 'B' will trigger display logic allowing them to see all 3 blocks. Here's my conundrum. My office is hiring a consultant to help us develop the questions for block 3 and they will not be ready at the time that we will be deploying the survey to contact list 'A'. So, hypothetically, I would like to go in and edit block 3, before deploying to group 'B'. The reason why were not sending two separate surveys is because we'd like all recipients to only get one survey ask, and so that we can easily analyze all responses to block 1 & 2 in Qualtrics. Anyone successfully accomplished this?