KUT = Key User Tool = Adaption mode for the Admin.
As for Field Update workflow rule, what you will have to do is create a field update on the business object that will store the Sales Org data. So if you are saying you want to create code list restrictions on the Sales Org data for the Opportunity screen, then the business object you will use here is the Opportunity. As for configuring the workflow conditions and actions, since the field update action can only accept values like text/integers/IDs/times/dates/codes and not variables, you will need to create a workflow rule for every sales org that could be determined in the Opportunity you want to set in the custom field.
Here is an example where on every save of the ticket, when the service team for the ticket changes for a specific service team, update a custom field = to the new service team value. In my example I had to create a workflow rule for every service team that is active in the solution. The custom field is then used to drive code list restrictions and HTML5 page layouts for a simple dynamic UI usecase to show/hide UI elements and make some of the UI elements mandatory based on a specific service team.
You of course could do all of this workflow logic with a few lines of SDK script, but that is the difference between a simple Admin rule editor vs. using SDK/Visual Studio to write script.