<Window x:Class="Sinix.TemplatedPartSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:templated="clr-namespace:Sinix.TemplatedPartControl;assembly=Sinix.TemplatedPartControl"
        Title="MainWindow"
        Height="398"
        Width="293">
  <StackPanel>
    <templated:SomeControl Margin="8" />
    <templated:SomeControl Margin="8">
      <templated:SomeControl.Resources>
        <ControlTemplate x:Key="{x:Static templated:SomeControl.HeaderTemplateKey}"
                         TargetType="Control">
          <Button Content="Changed part"
                  Style="{DynamicResource {x:Static templated:SomeControl.HeaderStyleKey}}" />
        </ControlTemplate>
      </templated:SomeControl.Resources>
    </templated:SomeControl>
    <StackPanel>
      <!-- Подменяемый шаблон можно определить где угодно -->
      <StackPanel.Resources>
        <ControlTemplate x:Key="{x:Static templated:SomeControl.HeaderTemplateKey}"
                         TargetType="Control">
          <CheckBox Content="Changed part - 2" HorizontalAlignment="Left"
                    Style="{DynamicResource {x:Static templated:SomeControl.HeaderStyleKey}}" />
        </ControlTemplate>
      </StackPanel.Resources>
      <templated:SomeControl Margin="8" />
    </StackPanel>
  </StackPanel>
</Window>