Hi. I am in China and want to stay longer. I already got enough visas in my A passport(is possible to get only 3 one month port office visas from Hong Kong) so they will not give me any more. They could give me another visa to my B passport(different nation and surname by one letter). But I have only one fingerprints so if they know I am the same person will that be ok or they will not let me enter? Thank You.

I don't think anyone here will be able to answer your question with any certainty. The details of your situation are unique and the answer may even vary from moment to moment, immigration officer to officer. I suggest you simply give it a try since the outcome will be the same, whether you run out of renewals or fail to be renewed on the 2nd passport.

Except that he runs the risk of being refused future entry on either passport if the officer notices.

Anything is possible which is why it's probably a better idea to stick to 1 passport, leave the territory and come back when he's legally entitled to do so.

Just to be clear, you can't stay in China longer, you can exit China and enter again with the other passport, probably. But you must exit with the same passport that you came in with. Not sure what the advantage of this is over getting a second visa in the same passport.

I presume you are not talking about extensions on a current visa, but exiting China and reapplying for a new visa. If you are being denied another visa in Passport A because you have too many, then that's a non-starter. If you want to try Passport B, go ahead BUT consider using a different application location (i.e. Macau instead of Hong Kong) and different entry port to what you usually use (Zhuhai instead of Shenzhen for instance). I doubt if the fingerprints are an important issue. Given that your birth date is presumably the same on both passports even if your name is slightly different, there's no guarantee that you'll get away with this but it's probably your only shot if you want to try to get back into China soon.

Very risky and kind of crazy idea.