Hi

You can retemplate the FieldItemControl in Blend and set the string you want.

Your template should be something like below:

<!--FieldItemControl-->
<Style TargetType="igPivotPrim:FieldItemControl" x:Key="DisableFilteringKey">
        <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="igPivotPrim:FieldItemControl">
                <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="2">
                    <VisualStateManager.VisualStateGroups>                        <VisualStateGroup x:Name="MeasureStates">
                            <VisualState x:Name="AllVisible"/>
                            <VisualState x:Name="Hidden">
                                <Storyboard>
                                    <DoubleAnimation Storyboard.TargetName="measureText" Storyboard.TargetProperty="Opacity" To="1"/>
                                    <DoubleAnimation Storyboard.TargetName="contentPresenter" Storyboard.TargetProperty="Opacity" To="0"/>
                                </Storyboard>
                            </VisualState>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
 
                    <Grid x:Name="Root" Background="Transparent">
                        <StackPanel Orientation="Horizontal">
                               <Border BorderBrush="DarkGray" BorderThickness="0" Background="Transparent">
                                <Grid>
                                <TextBlock Text="My Measures string" Opacity="0" Name="measureText" VerticalAlignment="Center" Margin="3, 0, 3,0"/>
  
                                <ContentPresenter Name="contentPresenter" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" />
                                </Grid>
                            </Border>
                            .........
                        </StackPanel>
                    </Grid>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>