There is no other way to use TransitionControl when changing the tabs except modifying the template of the TabControl.
If you don't want to use Blend, you can take the TabControl XAML from your installation folder, usually it is C://Program Files/Telerik/RadControls for Silverlight [version]/. Go to Themes folder and select the theme that you use in your application. Drill down to find the TabControl.xaml file in that directory.
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