Вы также можете сделать это со стилем,
<Style x:Key="PrettierDataGridStyle" TargetType="dg:DataGrid">
<Setter Property="CellStyle">
<Setter.Value>
<Style TargetType="dg:DataGridCell">
<Style.Triggers>
<!-- Highlight selected rows -->
<Trigger Property="IsSelected" Value="True">
<Setter Property="height" Value="35"></Setter>
</Trigger>
</Style.Triggers>
</Style>
</Setter.Value>
</Setter>
</Style>