@ZMac I wanted to share the Differentiated Tags FAQ.
As a former educator I understand your wanting to test out Differentiated Tags.
The FAQs mention that "you can filter the gradebook by Differentiation Tag to view and analyze the performance of specific student tag sets. Tags currently show under “Student Groups” in the traditional gradebook filter list". Given the limitation that Test Student cannot be assigned any assessments, an idea is you apply differentiated tags to your other students and you should be able to filter based on the assigned tags in Grades area.
Hope this pans out for you and you can share your experience. Have a great semester.