The following guide describes the process I went through to change the name shown in Startup Manager for the Boot Camp and macOS installations that I have on my external drive. The steps below might not work for your setup (for example, if you have Boot Camp installed on your internal drive). Proceed with caution, as you might not be able to reverse the changes (at least not easily).
- Open Terminal. Run the following command to list all external disks. Enter an administrator password if/when prompted.
sudo diskutil list external