Set proxy address to your Fiddler
Tap Search key on your phone
Look for the request to rwsettingblue.xml, websearch.exe use it to generate BingConfiguration_**-**.xml
I'm lazy to write how to write script to modify this file, but you can find similar thing from marass82's post.
I think these information is enough for every developpers.
You can always modify time on your phone to make websearch.exe request new xml from bing.com
I don't know the exact expiry time of this config xml cache (Maybe it will expiry within 1 day), but set one month ahead is enough and can ensure it update.