Business M Visa

I have just received my Chinese M type for a 30 days one year multiple entry one although I request for a max 180 days since 30 days would not be enough cause I would be traveling PRC most of the time. And it would be inconvenient if I have to rush out if the 30 days. I was earlier on given a 180 days before but now have reduce it to 30 days stay. Is there anything I can do to change or extend it. Thanks