I don't really see how them changing the name to troll is a problem. If they change the name to something stupid then you just leave the group.
Having the changes go through an admin though defeats the purpose of this suggestion... or am I missing something? Perhaps you change it and submit it for approval?
.. Except I'm sure people don't keep tabs on every social group they ever joined, they wouldn't even notice that they're a part of something that's potentially offensive/conflicting. Given the reasoning behind groups being dedicated to old usernames, I agree that there should be a way to change the group titles, but there should also be some way to monitor the changes (similar to how admins take requests for name-changes; requests go through them).