Override style in style - wpf

Question

Is it possible to override styles in other styles. My best description will be some non working code:
<Style x:Key="SpecialFont" TargetType="Label">
<Setter Property="Foreground" Value="Red" />
<Setter Property="FontSize" Value="28" />
</Style>
<Style TargetType="GroupBox">
<Setter Property="GroupBox.Resources">
<Setter.Value>
<Style x:Key="SpecialFont" TargetType="Label">
<Setter Property="FontSize" Value="74" />
</Style>
</Setter.Value>
</Setter>
</Style>
The idea is that I will define a style to my "special text", the font which by default is red and have a size at 28, but if the label is placed in a groupbox it should have the size at 74, but maintain the red color. How is this possible? I would prefer to have to same style-key in my xaml, and not create a style based on another, e.g. SpecialFontBig based on SpecialFont.
Edit:
Okay... Another explanation.
I want result like this:
<Style x:Key="BaseFont" TargetType="Label">
<Setter Property="Foreground" Value="White" />
</Style>
<Style x:Key="Font1" TargetType="Label" BasedOn="{StaticResource BaseFont}">
<Setter Property="FontSize" Value="10" />
</Style>
<Style x:Key="Font2" TargetType="Label" BasedOn="{StaticResource BaseFont}">
<Setter Property="FontSize" Value="20" />
</Style>
<Style x:Key="Font3" TargetType="Label" BasedOn="{StaticResource BaseFont}">
<Setter Property="FontSize" Value="30" />
</Style>
<Style x:Key="Font1Red" TargetType="Label" BasedOn="{StaticResource Font1}">
<Setter Property="Foreground" Value="Red" />
</Style>
<Style x:Key="Font2Red" TargetType="Label" BasedOn="{StaticResource Font2}">
<Setter Property="Foreground" Value="Red" />
</Style>
<Style x:Key="Font3Red" TargetType="Label" BasedOn="{StaticResource Font3}">
<Setter Property="Foreground" Value="Red" />
</Style>
Where FontX is used outside my groupboxes, and FontXRed is used inside them. Is it possible to overrule this foreground, without making a lot of FontXRed styles? For example something like:
<Style x:Key="BaseFont" TargetType="Label">
# IF INSIDE A GROUPBOX
<Setter Property="Foreground" Value="Red" />
# ELSE
<Setter Property="Foreground" Value="White" />
</Style>

Answer 1

Styles can be based on other styles -> http://msdn.microsoft.com/en-us/library/system.windows.style.basedon.aspx
<Style x:Key="Style1">
<Setter Property="Control.Background" Value="Yellow"/>
</Style>
<Style x:Key="Style2" BasedOn="{StaticResource Style1}">
<Setter Property="Control.Foreground" Value="Blue"/>
</Style>

Answer 2

I have created a new GroupBox, which solved my problem okay:
class MyGroupBox : GroupBox
{
public MyGroupBox()
{
var newForegroundSetter = new Setter(ForegroundProperty, Brushes.Black);
var stylesToUpdate = new List<string>
{
"TextBlockShared",
"SmallFontTextBlock",
"MediumFontTextBlock",
"LargeFontTextBlock",
"FontControlShared",
"SmallFontControl",
"SmallFontHeaderControl",
"MediumFontControl",
"MediumFontHeaderControl",
"LargeFontControl",
"LargeFontHeaderControl",
"SmallButton",
"MediumButton",
"LargeButton",
};
foreach (var styleKey in stylesToUpdate)
{
var existingStyle = FindResource(styleKey) as Style;
if (existingStyle == null) continue;
var newStyle = new Style(existingStyle.TargetType, existingStyle);
newStyle.Setters.Add(newForegroundSetter);
Resources.Add(styleKey, newStyle);
}
}
}

Answer 3

In case someone stumbles upon this, here is the trick that usually works for me.
Basically, I define a style inside another styles resources. I usually base the inner style on a key-referenced style to use it in other places, but you could place a plain simple style in there as well.
<Style x:Key="SpecialFont" TargetType="Label">
<Setter Property="Foreground" Value="Red" />
<Setter Property="FontSize" Value="28" />
</Style>
<Style TargetType="GroupBox">
<Style.Resources>
<Style TargetType="Label"
BasedOn="{StaticResource SpecialFont}" />
</Style.Resources>
</Style>