I have the same question. Basically I need to add a new entry to databases dictionary and be able to start using the new connection without restarting the service.

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    },
    'new_db': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'new_db_name',
        'USER': 'new_db_user',
        'PASSWORD': 'new_db_password',
        'HOST': 'new_db_host',
        'PORT': 'new_db_port',
    }
}