Change of subitem in WPF CustomControl Style?

Question

I have a CustomControl which contains among other things a DataGrid. One time I use this CustomControl I need to do a small change to the appearance of the DataGrid CellStyle.

What I am doing right now is Duplicating my whole CustomControl Style in XAML just to change the CellStyle. So I would like to keep my base cell style and only overwrite the DataGrid CellStyle. Therefore, I need to somehow access the DataGrid, is that possible?

Simplified Style for the CustomControl (DataGridCustomControl)

<Style TargetType="{x:Type local:DataGridCustomControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:DataGridCustomControl}">
                <DataGrid x:Name="part_datagrid" ItemsSource ="{Binding ItemsSource, RelativeSource={RelativeSource AncestorType={x:Type local:DataGridCustomControl}}}"
                <!-- some stuff which is always the same included here -->
                </DataGrid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

What I would like to do now is trying to change the properties of the datagrid in another Style. Essentially, something like shown below, which I could not get to work. (DataGridCellStyle1 not included here for abbreviation).

<Style x:Key="DataGridCustomControl1"  TargetType="{x:Type local:DataGridCustomControl}" BasedOn="{StaticResource {x:Type local:DataGridCustomControl}}">
    <Setter Property="DataGridCellStyle" Value="{StaticResource DataGridCellStyle1}"/>
</Style>

I actually don't have a clue if this may be achievable via ControlTemplates, but I wasn't able to get it on my own. So right now I'm not even sure, it is possible to access my part_datagrid.

<Style x:Key="DataGridCustomControl1"  TargetType="{x:Type local:DataGridCustomControl}" BasedOn="{StaticResource {x:Type local:DataGridCustomControl}}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type DataGridCell}">
            <!-- Implementation missing-->
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Answer 1

Add a DataGridCellStyle dependency property of type Style to your DataGridCustomControl class and bind to it in the ControlTemplate:

<ControlTemplate TargetType="{x:Type local:DataGridCustomControl}">
    <DataGrid x:Name="part_datagrid" CellStyle="{TemplateBinding DataGridCellStyle}" 
              ItemsSource ="...">
                <!-- some stuff which is always the same included here -->
    </DataGrid>
</ControlTemplate>

You can then set the DataGridCellStyle using a style setter, just like you would set any other dependency property.