One of my students found a way to amuse himself via changing his username continuously and writing something in the chat window as a doppelganger of somebody from the class. Is there a way to track down the username changes?
No, there is not.
Anyway, you could lock your meeting and allow only known people/names to enter the meeting.
In addition, you can kick him out if he is already in.
Well, it is possible to parse the GetMeetingParticipantEventsForMeeting response in JSON format to compare the AccountIds...