The only way to flash global into chinese nex without entering EDL is to patch global images in such way, so the bootloader in chinese phone can recognize it like a chinese version.
To enter EDL, phone disassembling and using PCB tespoints is required. Maybe there is a way to enter EDL using special service cable(USB_C contains a lot of methods for connected device identification). This cable(if it exists) can be only on the factory, ordinary service centers does not have it. Alternatively, appropriate fastboot command and an unlock code may be applicable - these adb tools just translate your commands to the host via driver and no more. So we need to disassemble bootloader code to get full commands and arguments list.