Extending Chinese visa

I will be studying in two different programs(one for this summer (june 10th to august) and another one for the fall (august to december)), but I do not have the visa document for the fall one yet. Since my friend is getting the visa for me in D.C. and it can only be this Tuesday, I will have to apply for only the summer one for now.

I was just wondering if I can extend the visa later by showing my document for the fall semester. I will be staying in beijing the whole time.