Posting on behalf of a customer.
Currently to get fields to show up in the “Additional fields” section in the Call to Action action in Rules Engine. CTA field would need to be marked editable within a given CTA Layout Configuration on a given CTA Type.

However that same field “Editable” Setting is used to allow an End User or CSM to modify the same field.
There are use cases where the field is only meant to be set by an automated method like rules engine, but isn’t meant for CSMs to edit, such as NPS Score and NPS Respondent Email. Therefore it be good to have a additional check box to allow edit from “Rule Engine” and another check box for “UI Editability”.