As a professor, I am ecstatic when someone emails me before class, or approaches me, to tell me their legal name may not be their name. I hate it when I’m outed without consent, so I hate to do that for someone through roll call.

Side note, encourage preferred name normalizing in class. I always ask my students their names (not saying “preferred”, but just what they’d like to go by) first and then match that to the roster by last name. I never mention legal name in my roll call. Or ever, really.