The section body is using the json-style k/v mapping, which makes it awkward to add new groups. You either have to continue to work in the json-style, or convert the existing data to yaml-style and then add the new groups.
An example:
Ideally this should look like:
# Editing object codfw/db2124 host_ip: 10.192.16.19 note: '' port: 3306 sections: s6: percentage: 100 pooled: true weight: 400