I don’t use Bluetooth with Blynk, but personally I just can’t get my head around the concept of shared access to a Bluetooth device in the way you’ve described.
Normally, with a Wi-Fi or Ethernet connected device, the communication route is that the device talks to the Blynk server across an internet connection, and the mobile device (phone/tablet) also talks to the Blynk server across an internet connection.
For the sake of this discussion, let’s say that the devices are located in your home.
When you share this project, the people you share this with have access to see the data that comes from the devices that are located in your home, and control them - regardless of where they are themselves.
The sharing process is there to give other people (and this is generally non-technical members of your household) the ability to control these Blynk connected devices without also giving those people the ability to edit the app project settings. That privilege is reserved for you as the account owner.
With Bluetooth, the connection is local because of the nature of the communication method, and the phone/tablet can act as a bridge between the Bluetooth device and the Blynk server (although I think this is optional, depending on whether an internet service is available and whether the direct connect option is used - I think).
When you share a Bluetooth project, I can’t see how the Bluetooth device(s) located in your home can be operated by the shared user, unless your phone is connected to that device.
What you’ve described is something very different, and it seems to me that what was actually needed was a clone of the project, and the Bluetooth device running a sketch with a different Auth code rather than the same one that your device uses.