convert.py

#!/usr/bin/env python3

from yaml import load, dump, FullLoader
import sys

file_name = sys.argv[1]

def process_ua(data):
    for node in data:
        if 'family_replacement' not in node:
            node['family_replacement'] = '$1'
        if 'v1_replacement' not in node:
            node['v1_replacement'] = '$2'
        if 'v2_replacement' not in node:
            node['v2_replacement'] = '$3'
    with open('ua.yaml', 'w') as stream:
        dump(data, stream)

def process_os(data):
    for node in data:
        if 'os_replacement' not in node:
            node['os_replacement'] = '$1'
        if 'os_v1_replacement' not in node:
            node['os_v1_replacement'] = '$2'
        if 'os_v2_replacement' not in node:
            node['os_v2_replacement'] = '$3'
        if 'os_v3_replacement' not in node:
            node['os_v3_replacement'] = '$4'
        if 'os_v4_replacement' not in node:
            node['os_v4_replacement'] = '$5'
    with open('os.yaml', 'w') as stream:
        dump(data, stream)

def process_device(data):
    for node in data:
        if 'device_replacement' not in node:
            node['device_replacement'] = '$1'
        #if 'brand_replacement' not in node:
        #    node['brand_replacement'] = '$2'
        if 'model_replacement' not in node:
            node['model_replacement'] = '$1'
    with open('device.yaml', 'w') as stream:
        dump(data, stream)

with open(file_name, 'r') as file:
    data = file.read()
    yml = load(data, Loader=FullLoader)
    process_ua(yml['user_agent_parsers'])
    process_os(yml['os_parsers'])
    process_device(yml['device_parsers'])
                                            

You don't processed regex_flag key of device_parsers, example, here.
You need to add the following code, like here:

...
def process_device(data):
    for node in data:
        if 'regex_flag' in node:
            node['regex'] = f'(?{node["regex_flag"]}:{node["regex"]})'
        if 'device_replacement' not in node:
            node['device_replacement'] = '$1'
        ...