I've found that since you can't use BasedOn on a DynamicResource, you can „convert“ the DynamicResource to StaticResource by merging the ResourceDictionary holding your „parent“ resources to your current Window/UserControl/whatever. This way you are now able to refer to the resource object (eg. Style) using StaticResource. This way you can use Datatriggers on DynamicResource (through conversion).

Example:

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/MyProject.Styles;component/ButtonStyles.xaml"/>
        </ResourceDictionary.MergedDictionaries>
        [*Your other resources can be put here*]
    </ResourceDictionary>
</Window.Resources>

…

<Button Command="{Binding MyCommandInViewModel, RelativeSource={RelativeSource AncestorType=Window}}">
    <Button.Style>
        <Style BasedOn="{StaticResource StyleFromButtonStyles}" TargetType="Button">
            <Style.Triggers>
                <DataTrigger Binding="{Binding SomeBool}" Value="True">
                    <Setter Property="Button.Content" Value="{StaticResource SomeImage}"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding SomeBool}" Value="False">
                    <Setter Property="Button.Content" Value="{StaticResource SomeOtherImage}"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Hence Datatriggers are applied to a button styled in an imported ResourceDictionary.

The listbox itself is reacting to the double click, but only in the part of it's area that is not covered by a list box item.

You need the event handler to be tied to the listboxitem.

public class ControlItemDoubleClick : DependencyObject {
public ControlItemDoubleClick()
{
 
}
 
public static readonly DependencyProperty ItemsDoubleClickProperty =
	DependencyProperty.RegisterAttached("ItemsDoubleClick",
	typeof(bool), typeof(Binding));
 
public static void SetItemsDoubleClick(ItemsControl element, bool value)
{
	element.SetValue(ItemsDoubleClickProperty, value);
 
	if (value)
	{
		element.PreviewMouseDoubleClick += new MouseButtonEventHandler(element_PreviewMouseDoubleClick);
	}
}
 
static void element_PreviewMouseDoubleClick(object sender, MouseButtonEventArgs e)
{
	ItemsControl control = sender as ItemsControl;
 
	foreach (InputBinding b in control.InputBindings)
	{
		if (!(b is MouseBinding))
		{
			continue;
		}
 
		if (b.Gesture != null
			&& b.Gesture is MouseGesture
			&& ((MouseGesture)b.Gesture).MouseAction == MouseAction.LeftDoubleClick
			&& b.Command.CanExecute(null))
		{
			b.Command.Execute(null);
			e.Handled = true;
		}
	}
}
 
public static bool GetItemsDoubleClick(ItemsControl element)
{
	return (bool)element.GetValue(ItemsDoubleClickProperty);
}

<ListBox Name="SmallVideoPreviews" Grid.Column="1" MaxHeight="965"
    ItemsSource="{Binding BrowseVideos}" 
    myStuff:ControlItemDoubleClick.ItemsDoubleClick="true"
    ItemTemplate="{StaticResource BrowseTemplate}">
    <ListBox.InputBindings>
        <KeyBinding Key="p" 
            Command="{Binding PlayVideoCommand}"
            CommandParameter="{Binding ElementName=SmallVideoPreviews, Path=SelectedItem}"/>
        <MouseBinding Gesture="LeftDoubleClick"
            Command="{Binding PlayVideoCommand}"
            CommandParameter="{Binding ElementName=SmallVideoPreviews, Path=SelectedItem}"/>
    </ListBox.InputBindings>
</ListBox>

or

You can add a style to ListBox.ItemContainerStyle, and add an EventSetter there:

<ListBox>
    ....
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}" BasedOn="{StaticResource {x:Type ListBoxItem}}">
            <EventSetter Event="MouseDoubleClick" Handler="ListBoxItem_MouseDoubleClick"/>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

ListBoxItem_MouseDoubleClick is a method in your code behind with the correct signature for MouseDoubleClick.