hey there.,

a couple of things to add to masters post.

british passports seem to be more favoured and can change from L visa to Z visa without leaving china, (but only in certian provinces)

you could use an agent in china to change frmo an L visa to a Z visa (some can do it some cant)

I am currently on a residency permit for a job that i left. from my understanding as long as you dont get the canceled stamp in your passport they cant easily cancel your residency permit.
if you pi$$ off an employer enough, they will spend the time and money to do it, but its very very VERY hard for an employer to cancel a residency permit without your passport.
so if you dont annoy them too much they tend to cancel you expert certificate but leave you residency permit intact as the head ache is not worth it.

I left my last job in bad grounds and i know they wanted to cancel my rp, i still check into hotels from time to time so im sure if my rp was canceled a member of the PSB would have come to the hotel to take my passport away and change to an L visa.

A way around having to change RPs is to say to the new school you can work part time (part time being however many hours they need you) then you shouldnt need to get a new rp with them as you are only on a part time contract.

stay safe and be lucky.
the best way to do it is to find a clause in the contract they have broken and cancel the contract because of that (even a minor thing)
also you can look up SAFEA rules (SAFEA gives them the power to hire westerners) and if they have broken one of them, you can tell them they have not kept up with that so the contract is void.

needs be, find someone who knows the system and bring them to your office to talk with your boss (make sure who ever it is is a male as men are in general not pushovers, also a chinese friend of yours would not want to loose face infront of you, a western friend who knows the rules can walk in and after 20 minutes have the school beging for the SAFEA release documents to get you as far away from them as possible)

stay safe and research every school before signing a contract.