Bind template data field to instance (via "Use a custom path expression"?) - wpf

Question

I have created a template of a button, which contains an Image and a TextBlock. Since I would like to change the appearance of both, I think they need to be in the Template. But, of course, not every instance of this template should present the same text and image.
Until now, i found a promising property called "Use a custom path expression" at the "Text" / "Source"-value filed of the TextBlock / Image at:
Data Binding... > Element Property > Use a custom path expression
I would now like to set this value at the instances of the button. I already tried to manually insert a myText="Lorem Ipsum" in the XAML of the Button, but that does not seem to work.
Thank you in advance for your help!
Update: This is, how the XAML looks like:
<TextBlock [...] Text="{Binding myText, ElementName={x:Null}, FallbackValue=Lorem}"/>
How do I access this or modify this, so it can be accessed?
Update 2: There already exist bindings for the TextBlock and the Image. At the moment, the XAML of the Button looks like that:
<s:SurfaceButton Command="{Binding SearchCustomCommand}" Style="{DynamicResource BasicButton}">
<StackPanel Orientation="Vertical" Height="60" Width="48" IsHitTestVisible="False">
<Image Source="{StaticResource ImageSourceToolboxSearchIcon}"
[...]
Stretch="Uniform" />
<TextBlock Text="{lex:LocText ToolboxButtonSearchesCustom}"
FontFamily="{DynamicResource button.font}"
[...]
FontSize="{DynamicResource button.size}"
Foreground="{DynamicResource button.color.default}"/>
</StackPanel>
</s:SurfaceButton>
I would now like to extract the Image and Textbox to the template (which also already exists), so I could refrence the Button in a way like this (whith all the Information about sizes and colors etc in the template and only the reference to the resource in the actual instance of the button - to be able to change the image/text for echt button seperately):
<s:SurfaceButton
Command="{Binding SearchPopularCommand}"
Style="{DynamicResource ToolboxButtonBig}"
ImageSource="{StaticResource ImageSourceToolboxSearchIcon}"
TextBlockSource="{lex:LocText ToolboxButtonSearchesCustom}"/>
I already copied the whole XAML for the StackPanel and the included TextBlock and Image to the Template. Now those are shown on every Button (which is fine), but i can't change the contents of them.
I'm sorry if the description is quite poor - I'm rather new to WPF...
Update 3: After some further research, I found questions similar to mine - which obviously describe the problem better than I could:
Button template with image and text in wpf
Creating an image+text button with a control template?

Answer 1

it is not necessary to edit button's template to insert image and text, you can set Button.Content property like this:
<Button>
<Button.Content>
<StackPanel Orientation="Horizontal">
<Image Source="../Images/image.png"/>
<TextBlock Text="Lorem Ipsum"/>
</StackPanel>
</Button.Content>
</Button>
and it will work well. example above can be simplified but I inserted it like this for better understanding what is going on.
EDIT:
here are examples how it can be done in two different ways:
overwriting template:
<Button Content="Lorem Ipsum">
<Button.Template>
<ControlTemplate TargetType="Button">
<StackPanel Orientation="Horizontal">
<Image x:Name="ButtonImage" Source="../Images/mouseNotOverImage.png"/>
<ContentPresenter Margin="2"
HorizontalAlignment="Center"
VerticalAlignment="Center"
RecognizesAccessKey="True" />
</StackPanel>
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter TargetName="ButtonImage" Property="Source" Value="../Images/mouseOverImage.png"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Button.Template>
</Button>
complete button template definition you can find here
modifying style:
<Button>
<Button.Style>
<Style TargetType="Button">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Content">
<Setter.Value>
<StackPanel Orientation="Horizontal">
<Image Source="../Images/mouseOverImage.png"/>
<TextBlock Text="Lorem Ipsum"/>
</StackPanel>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsMouseOver" Value="False">
<Setter Property="Content">
<Setter.Value>
<StackPanel Orientation="Horizontal">
<Image Source="../Images/mouseNotOverImage.png"/>
<TextBlock Text="Lorem Ipsum"/>
</StackPanel>
</Setter.Value>
</Setter>
</Trigger>
</Style.Triggers>
</Style>
</Button.Style>
</Button>

Answer 2

Your first option would be to define a style (or styles), e.g.
<Window.Resources>
<Style x:Key="MyButton" TargetType="{x:Type Button}" >
<Setter Property="Content">
<Setter.Value>
<Grid>
<Image .../>
<TextBlock Text="Test"/>
</Grid>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<Button Style="{StaticResource MyButton}" />
</Grid>
Your second option would be to use Blend to make a copy of the default button style and edit that
<Window.Resources>
<Style x:Key="MyButton" TargetType="{x:Type Button}" >
<Setter Property="Content">
<Setter.Value>
<Grid>
<TextBlock Text="Test"/>
</Grid>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="ButtonFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="2" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<LinearGradientBrush x:Key="ButtonNormalBackground" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#F3F3F3" Offset="0"/>
<GradientStop Color="#EBEBEB" Offset="0.5"/>
<GradientStop Color="#DDDDDD" Offset="0.5"/>
<GradientStop Color="#CDCDCD" Offset="1"/>
</LinearGradientBrush>
<SolidColorBrush x:Key="ButtonNormalBorder" Color="#FF707070"/>
<Style x:Key="MyButtonStyle" TargetType="{x:Type Button}">
<Setter Property="FocusVisualStyle" Value="{StaticResource ButtonFocusVisual}"/>
<Setter Property="Background" Value="{StaticResource ButtonNormalBackground}"/>
<Setter Property="BorderBrush" Value="{StaticResource ButtonNormalBorder}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Padding" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Themes:ButtonChrome x:Name="Chrome" BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}" RenderDefaulted="{TemplateBinding IsDefaulted}" SnapsToDevicePixels="true">
<!-- put your text and image here -->
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Themes:ButtonChrome>
<ControlTemplate.Triggers>
<Trigger Property="IsKeyboardFocused" Value="true">
<Setter Property="RenderDefaulted" TargetName="Chrome" Value="true"/>
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="true">
<Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#ADADAD"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<Button Content="Button" HorizontalAlignment="Left" Margin="167,151,0,0" VerticalAlignment="Top" Width="75" Style="{DynamicResource MyButtonStyle}"/>
</Grid>
and a third option would be to create a custom control based on the default button style. You could then create dependency properties and use template bindings.