Way to change Google Chrome user agent in Selenium?

You should use ChromeOptions from selenium.webdriver:

from selenium import webdriver

chrome_options = webdriver.ChromeOptions()
chrome_options.add_argument('--user-agent="Mozilla/5.0 (Windows Phone 10.0; Android 4.2.1; Microsoft; Lumia 640 XL LTE) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Mobile Safari/537.36 Edge/12.10166"')
driver = webdriver.Chrome(chrome_options=chrome_options)

This should work.

A simple way to use a random User Agent would be using Python's fake_useragent module as follows :

from selenium import webdriver
from selenium.webdriver.chrome.options import Options
from fake_useragent import UserAgent

options = Options()
ua = UserAgent()
userAgent = ua.random
print(userAgent)
options.add_argument(f'user-agent={userAgent}')
driver = webdriver.Chrome(chrome_options=options, executable_path=r'C:\WebDrivers\ChromeDriver\chromedriver_win32\chromedriver.exe')
driver.get("https://www.google.co.in")
driver.quit()

Result of 3 consecutive execution is as follows :

1. First Execution :

   Mozilla/5.0 (Windows NT 4.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2049.0 Safari/537.36
   

2. Second Execution :

   Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.517 Safari/537.36
   

3. Third Execution :

   Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1309.0 Safari/537.17