I am looking at the Phison 2307 Controller on USB 3.0 flash storage devices, I have seen a few examples using a Phison 2303 controller which have successfully updated and modified. I am interested to know how is this functionality is removed with the updated controller?
I don't have any specific knowledge of that controller, but I have read about DFU and have experience with USB firmware. If you are developing new firmware and have the source code, you can remove the DFU USB descriptors and remove the code that handles getting into bootloader mode, and it would effectively be disabled. There might be some other way to get into the bootloader though, like driving a certain pin high at power up.