As far as I understand you need to change the default hover effect of the control. Your snippet in not going to work because the default template triggers/visualStates are applied after the style triggers, hence the trigger becomes overridden. In other words you can not apply two styles at the same time.
In order to customize the default hover state you have to edit the default template of the control. For your convenience I have extracted the template using Blend (as described in this article
) in the attached project. Please take a look at it and let me know if it works for you.
Pavel R. Pavlov
the Telerik team