Is it possible to "change" from day to night ?  If you comply with the requirements of a work visa, you will get one, and the X visa will be cancelled.  If because you have an X visa you think you will be given a Z visa by just asking, then the answer is no.

Where do these people come from? You will have to exit China in order to do this. Have a job, contract, foreign expert certificate, and medical exam. It is all on the website of the PSB. Have a look.

Yeah, but you have to either exit China, or go back to your home country depending on the situation. Your employer will set this up, and a good one will pay for the the flight and visa costs.

Source: my school offered this.

I've heard Shandong province can get you a visa switched without leaving the country. Can any Shandongers verify this?