China Visa Extension

Dear Sir,

Good Evening. I am David, from Malaysia.
I will cross border from Nepal - Tibet. My tour agent has assisted us to apply the Tibet Permit with 30 inclusive day China Tourist L. The tour guide told us they cant apply 6 months L with multiple entry. However,my return flight from Beijing to Malaysia is on 16th September.

Please advise whether i could extend my 30 days L to 6 months L with multiple entry in Xi An? China Government stated that:

Foreign citizen who needs to stay in China longer than the duration of stay permitted by the visa must apply for an extension of stay at a local public security bureau before the original permitted period of stay expires. This does not necessarily mean your application for an extension will be approved. << The last paragraph actually concerns me whether i could extent it before it expires.

Please Advise.

Thanks & Regards,
David