Hi Aniket,

You can include the Theme XAML in your application and use it directly instead of setting the Theme property on the XamDataGrid itself.  Just add the ResourceDictionaries from the DefaultStyles folder located here:

C:\Program Files (x86)\Infragistics\2013.2\WPF\DefaultStyles\DataPresenter

You only need to add the dictionaries that belong to the style you want to use.  You will also need to include their dependencies.  For example, the normal Metro theme requires the following dictionaries:

DataPresenterGeneric.xaml

DataPresenterGeneric_Brushes.xaml

DataPresenterGeneric_Express.xaml

DataPresenterMetro.xaml

DataPresenterMetro_Brushes.xaml

DataPresenterMetro_Express.xaml

In your App.xaml, you can add the DataPresenterMetro.xaml ResourceDictionary so it applies to all XamDataGrids in the application. 

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Themes\DataPresenterMetro.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

From this point on you can modify the theme xaml as you like.