Not with default vB. There might be a modification for this, otherwise you could just change it in the database using phpMyAdmin or such.
Maybe a better alternative would be to either:
- Moderate new threads in this forum. If accepted by staff, the original poster is still on the thread.
- Have a submission forum where members only see their own threads. If accepted staff can move the thread to public forums (still with original author). This is how we do this with article submissions:
Submit New Article