Currently Expression Blend will generate the styles with the brushes and resources inline. If you wish to have all resource brushes separately in your resource dictionary, you can use the one from the Themes_WPF solution shipped with the suite. Choose the one that corresponds to the theme you have chosen as a base for your customizations. I attach here a copy of the default Office Black theme for RadDateTimePicker.
In any case, you will need to modify or override each brush manually. You can modify the existing ones, or replace them with your own, but still you will need to do that for one brush at a time.
Hope this helps.
the Telerik team
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