Currently, Roles define which users can make an Order Status change.

How can I apply Roles to Status Transitions?

User Roles allow you to define which backend users can make an Order Status change. For example, you might want to only allow users in the "Shipping Clerk" group transition an order from the Paid to Shipped status.

First, define a Role under Administration > Roles in the backend.

then, apply this to a User. Goto Administration > Users, and select the desired User Role.

Now, if you goto Business Settings > Order Statuses, you can select permissions for the Shipping Clerk. In the example below, we'll only allow the Shipping Clerk to define the "Paid" status transition as "Shipped":