<Style TargetType="{x:Type Primitives:RowSelectorHeaderCellControl}" x:Key="Test">
<Setter Property="ContentTemplate">
<Setter.Value>
<DataTemplate >
<Button Background="YellowGreen" Content="ColChooser" Name="button1" Click="button1_Click" />
</DataTemplate>
</Setter.Value>
</Setter>
</Style>