Extending 60 day limit on 10 year visa

I am an Emeritus Professor at the University of California have a 10 year visa that expires in 2028, with a 60 day limit per visit. I may be teaching and conducting research at China Agricultural University, Zhejiang University and Southwest University next year and the estimated time for my visit may exceed 60 days. Will it be possible to extend the 60 days to 120 days on this visa or to ask for an extension once I am in China?