Currently all YAML job templates are read-only. A generated document will be shown, and allow for a syntax check, but changes can't be saved.
The editor, hidden by default, should migrate the job template the first time it's saved and hide the legacy UI. From that point only YAML can be used to make changes, whether it's through UI or API.
Basic verification of the last state will ensure that saving changes results in an error if the same YAML was changed in the interim.