Since Q1 2011, the Style / ControlTemplate of the RadExpander has been improved (now it is much smaller than the one from Q3 2010). Previously there used to be two templates that control the Header part of the Expander which was a bad design. Here you can find the new Template structure of the RadExpander. In order use your custom Template , now you have to edit the Template of the Expander and change dynamically the whole Style. Please let us know if you need further assistance on this.
the Telerik team
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