In general, no part that isn't "available" for coming "out" would be able to do so just by being called by name... there seems to be an inner self-helper or at least a part that is "deciding" who needs to be out when.. in general .. imo. I would see no reason for trying to have someone switch if you had discussed this previously with another part, i.e. that the one you "know" needs to be the one who drives and if another is "out" and going to try and drive, why not "call the name" of the one who is supposed to drive? Kinda of like helping them stay focused, or centered, on the task at hand. For safety..

But I agree, it needs to be discussed.. maybe even a topic for their system to discuss first? And if thereare "littles" and an adult knows there will be fun ...again, if agreed upon, why not acknowledge their littles names and play? Maybe because.....

The problem most see and why they say only by a professional, is that if someone, without permission, try forcing a part to come forward or "out" then what do you do if an angry part comes out instead, or a self injurious part, are you able to deal with that? There needs to be some agreement with the host or original, if you know who that is (or whomever is your friend), and some way for you to facilitate THEM to control which part will be allowed to speak, play etc. Perhaps you could go to a few sessions with your friend, and learn from the therapist who what why and why not????