To change the default Raspberry Pi BLE name we will use machine-info. You can change the pretty hostname variable in the machine-info

$ sudo nano /etc/machine-info

PRETTY_HOSTNAME=<Friendly Machine Name>

You need to restart the bluetooth service:

$ sudo systemctl reload-or-restart bluetooth

Machine Info Man Page

$ man machine-info
MACHINE-INFO(5)                            machine-info                           MACHINE-INFO(5)

NAME
       machine-info - Local machine information file

SYNOPSIS
       /etc/machine-info

DESCRIPTION
       The /etc/machine-info file contains machine metadata.

       The basic file format of machine-info is a newline-separated list of environment-like
       shell-compatible variable assignments. It is possible to source the configuration from
       shell scripts, however, beyond mere variable assignments no shell features are supported,
       allowing applications to read the file without implementing a shell compatible execution
       engine.

       /etc/machine-info contains metadata about the machine that is set by the user or
       administrator.

       Depending on the operating system other configuration files might be checked for machine
       information as well, however only as fallback.

       You may use hostnamectl(1) to change the settings of this file from the command line.

OPTIONS
       The following machine metadata parameters may be set using /etc/machine-info:

       PRETTY_HOSTNAME=
           A pretty human-readable UTF-8 machine identifier string. This should contain a name
           like "Lennart's Laptop" which is useful to present to the user and does not suffer by
           the syntax limitations of internet domain names. If possible, the internet hostname as
           configured in /etc/hostname should be kept similar to this one. Example: if this value
           is "Lennart's Computer" an Internet hostname of "lennarts-computer" might be a good
           choice. If this parameter is not set, an application should fall back to the Internet
           host name for presentation purposes.

       ICON_NAME=
           An icon identifying this machine according to the XDG Icon Naming Specification[1]. If
           this parameter is not set, an application should fall back to "computer" or a similar
           icon name.

       CHASSIS=
           The chassis type. Currently, the following chassis types are defined: "desktop",
           "laptop", "server", "tablet", "handset", "watch", and "embedded", as well as the
           special chassis types "vm" and "container" for virtualized systems that lack an
           immediate physical chassis. Note that many systems allow detection of the chassis type
           automatically (based on firmware information or suchlike). This setting (if set) shall
           take precedence over automatically detected information and is useful to override
           misdetected configuration or to manually configure the chassis type where automatic
           detection is not available.

       DEPLOYMENT=
           Describes the system deployment environment. One of the following is suggested:
           "development", "integration", "staging", "production".

       LOCATION=
           Describes the system location if applicable and known. Takes a human-friendly,
           free-form string. This may be as generic as "Berlin, Germany" or as specific as "Left
           Rack, 2nd Shelf".

EXAMPLE
           PRETTY_HOSTNAME="Lennart's Tablet"
           ICON_NAME=computer-tablet
           CHASSIS=tablet
           DEPLOYMENT=production

SEE ALSO
       systemd(1), os-release(5), hostname(5), machine-id(5), hostnamectl(1), systemd-
       hostnamed.service(8)

NOTES
        1. XDG Icon Naming Specification
           http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html

systemd 232                                                                       MACHINE-INFO(5)