After upgrading OS X to version 10.4.1 Tiger I am not able to set XML files to open with Oxygen when I click Change All in the Get Info dialog. This worked in OS X 10.3.x.
<key>CFBundleIdentifier</key> <string>ro.sync.exml.Oxygen</string>and restart Oxygen. Now you can select Change All in the Get Info dialog to make the association.