I did try and see if you could modify the default desired capabilities for Chrome and use Open Browser instead of Create Webdriver.
When using Open Browser, desired_capabilities and chrome_options are both None for Chrome's __init__.
In this scenario, a ChromeOptions instance is constructed and to_capabilities is used to convert to desired capabilities.
The to_capabilities method always replaces the chromeOptions entry in the desired capabilities dict.
In other words, storing any chrome options in the default desired capabilties (
selenium.webdriver.DesiredCapabilities.CHROME) has no effect.
FYI the desired capabilities entry for the Chrome option test-type looks like this:
'chromeOptions': {'args': [u'test-type'], 'extensions': []}