Пример кода того, что сказал dnr3, шаблонная кнопка ToggleButton
<Style x:Key="BoldWhenClickedTextBlock" TargetType="ToggleButton" BasedOn="{StaticResource {x:Type ToggleButton}}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<TextBlock x:Name="c_toggleButtonTextBlock" Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type ToggleButton}}, Path=Content}"/>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsMouseOver" Value="True">
<Setter TargetName="c_toggleButtonTextBlock" Property="TextDecorations" Value="Underline"/>
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="True">
<Setter TargetName="c_toggleButtonTextBlock" Property="FontWeight" Value="Bold" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
А затем ToggleButton "TextBlock" может использовать это с
<ToggleButton Style="{StaticResource BoldWhenClickedTextBlock}" Content="My Text.."/>