Transforming a tourist L into a student visa

Hello,

I will start my year abroad at Zhejiang university in September, and I would like to go to China in June, then travel to Vietnam and come back in August to start my studies. Do you know if this is possible ? Could I apply for a multi-entry tourist L and then change it into a student X/residence permit while in China ? Or could I apply my student X in Vietnam ?

Thanks a lot,

Romain