Once I create a data-driven segment, can I edit it manually?

Hey there,

You can’t manually add people to a data-driven segment, but it sounds like maybe you could benefit from a manual segment for this kind of situation (manual updating). 

These links go into more detail about both Data-driven Segment and Manual Segment types, and the most relevant parts for your question are:
 

Data-driven segments are groups of people that you automatically populate when they meet certain conditions. People enter the segment when they match the conditions and leave the segment when they stop matching the conditions.

Manual segments let you group people according to business logic outside of Customer.io. As the name suggests, you’ll add people to, and remove people from, these segments manually—through a CSV upload, part of a campaign workflow, or using our API.

So, if the manual updating you’re trying to do is something that would be best handled by a manual segment, I would recommend switching to this set-up. Data-driven segments are designed to remove the manual elements completely, so you’ll need to rely on their logic to do any removal or adding of profiles.

Hope this helps explain how this all works!