code.xaml

        <ControlTemplate x:Key="SimpleTemplate">
            <StackPanel Orientation="Horizontal">
                <StackPanel Margin="7 0 0 0">
                    <TextBlock Margin="0 0 0 0"
                               Text="{Binding Name}"
                               FontSize="12" />
                    <TextBlock Text="{Binding Status}"
                               FontSize="12" />
                </StackPanel>
            </StackPanel>
        </ControlTemplate>
        <ControlTemplate x:Key="ExtendedTemplate">
            <StackPanel Orientation="Horizontal">
                <StackPanel Margin="15 0 0 0">
                    <TextBlock Margin="0 0 0 0"
                               Text="{Binding Name}"
                               FontSize="11"
                               FontWeight="Bold" />
                    <TextBlock Text="{Binding Status}"
                               FontSize="11" />
                </StackPanel>
            </StackPanel>
        </ControlTemplate>
        <DataTemplate x:Key="MyTemplate">
            <Control x:Name="theControl"
                     Focusable="False"
                     Template="{StaticResource ExtendedTemplate}" />
            <DataTemplate.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ComboBoxItem}}, Path=IsSelected}"
                             Value="True">
                    <Setter TargetName="theControl"
                            Property="Template"
                            Value="{StaticResource SimpleTemplate}" />
                </DataTrigger>
            </DataTemplate.Triggers>
        </DataTemplate>