In order to set the Expander Button position you have to make changes in its style. You should modify the ControlTemplate "ExpanderHeaderTemplate" and to set the RadExpanderDecorator`s property HorizaontalAlignment to Right .
I prepared a sample project demonstrating this style changes. I hope this is what you need .
Please let me know if you need more info and I would be glad to assist you further.
All the best,
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items