Este es el código de la página web de MSDN, que creo que va a ayudar a (http://msdn.microsoft.com/en-us/library/system.windows.controls.textblock.aspx).
XAML
<TextBlock Name="textBlock1" TextWrapping="Wrap">
<Bold>TextBlock</Bold> is designed to be <Italic>lightweight</Italic>,
and is geared specifically at integrating <Italic>small</Italic> portions
of flow content into a UI.
</TextBlock>
<Button Width="100" Margin="10">Click Me</Button>
<TextBlock Name="textBlock2"
TextWrapping="Wrap" Background="AntiqueWhite" TextAlignment="Center"
>
By default, a TextBlock provides no UI beyond simply displaying its contents.
</TextBlock>
<Button Width="100" Margin="10">Click Me</Button>
C#
TextBlock textBlock1 = new TextBlock();
TextBlock textBlock2 = new TextBlock();
textBlock1.TextWrapping = textBlock2.TextWrapping = TextWrapping.Wrap;
textBlock2.Background = Brushes.AntiqueWhite;
textBlock2.TextAlignment = TextAlignment.Center;
textBlock1.Inlines.Add(new Bold(new Run("TextBlock")));
textBlock1.Inlines.Add(new Run(" is designed to be "));
textBlock1.Inlines.Add(new Italic(new Run("lightweight")));
textBlock1.Inlines.Add(new Run(", and is geared specifically at integrating "));
textBlock1.Inlines.Add(new Italic(new Run("small")));
textBlock1.Inlines.Add(new Run(" portions of flow content into a UI."));
textBlock2.Text =
"By default, a TextBlock provides no UI beyond simply displaying its contents.";
Gracias por tanto las grandes respuestas. Upvoted ambos. Elegí la que hice porque era específica para mi ejemplo. – Vaccano
Más solución mejor: http://stackoverflow.com/questions/947614/changing-label-properties-programmatically – digz6666