I was trying to disable Silverlight caching in IIS 7, and when i deployed my solution to Windows 2008 Ent. in Windows Azure. Every time you click on the xap file that i need to disable caching on it by checking expire web content immediately after i clicked on Set Common Headers link on the right pane, the web.config is not being updated at all. but this works on my local IIS.
I ended up with adding this attribute that has been added my local IIS to web.config and deploy it so i don't need to do this every time i perform a deployment.
<clientCache cacheControlMode="DisableCache" />
To disable caching in Silverlight "xap" file from IIS, Here is the article that i'm referring to:
Hope this tip helps.