If you wish to convert foreign currency into RMB, go downtown to one of the major branches of the Bank of China, but not at weekends. Opening hours of the bank are likely to be from 8.30 am until 6 pm, but winter opening hours will probably be somewhat different. Remember to take your passport with you.

Not always, it differs. Some will, some won't. Easier to get a chinese friend you know and trust, to use their ID to change it for you.

I thought that Chinese banks were always eager to obtain the likes of US dollars. So,I'm somewhat surprised by what you have posted re that. But of course, I am aware that the other way around would indeed be a problem without approval from your school/college/university/training centre.
Thanks for your input re the above and also re my other tips. It's all good stuff for the rest of us.