No, it is not possible to do that legally because the 'Z' visa is linked to your current WP/FEC which is employer specific. Therefore, you cannot legally have a second income on the visa and residence permit.

Should you decide to quit your current post and go into the restaurant business, you or your employer would have to cancel your RP. You would then probably have to leave the country and obtain a 'L' or 'F' visa long enough for you to open the business, get all of the restaurant licencing requirements including official company stamps, undergo the mandatory medical examination, apply for an Alien Workers Licence attached to your new business, leave the country again, obtain a new 'Z' visa, return and apply for a new WP/FEC and RP all connected to your new job title and company.

I would also suggest that you get very clear guidance from a qualified lawyer or business consultant about the implications of firstly opening a food business and getting the appropriate licencing (this is more complex than other forms of business such as trading because of food safety. The Chinese government are now severely screwing down on new food producers and distributors).

Secondly, you need to be very clear about the implications of being an equity partner with a Chinese partner. Legal partnerships in China are not so transparent as in the west. They can be fraught with danger especially for the western partner. Regardless of how much you like or trust your partner, you should be aware that legally they will have more rights than you even if you have put up most of the capital.

are uu nuts a chinese partner beware of the smile it will fool u the backstabbers good luck

also i would rather flusch my money down the toilet