I had similar problem recently in two column grid, I needed a margin on elements in right column only. All elements in both columns were of type TextBlock.
<Grid.Resources>
<Style TargetType="{x:Type TextBlock}" BasedOn="{StaticResource OurLabelStyle}">
<Style.Triggers>
<Trigger Property="Grid.Column" Value="1">
<Setter Property="Margin" Value="20,0" />
</Trigger>
</Style.Triggers>
</Style>
</Grid.Resources>