Selenium Webdriver: Override IOS Safari user agent

I'm using Selenium webdriver with Python and my purpose is to override the default Safari browser user agent in a remote iPhone device.

I've done it with Safari browser on a remote Mac. as follows:

 driver = webdriver.Remote(
       command_executor=SAUCELABS_DESKTOP,
        desired_capabilities=safari_caps,
    )

where safari_caps contains a gist that execute defaults write com.apple.Safari CustomUserAgent 'my_custom_user_agent'. This works fine.

I was trying the same with the IOS Safari version but is not overriding the user agent. Is there something that I missed?

Thanks a lot!