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Change property of controls child object by using Styles or DataTemplate in WPF application

Let's say I have a button and I have an image (though it could be any controls) inside of it:
<Button Width="150" Height="80">
<Image Source="..." Width="50" Height="50" />
</Button>
I want to change the style of button when mouse is over it and make it so that I could also change properties of the image inside when it happens.
<Style TargetType="Button">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Opacity" Value="0.5" />
<!-- Here I want to change alignment of the image inside the button if there is one -->
<Setter Property="Image.HorizontalAlignment" Value="Right" />
</Trigger>
</Style.Triggers>
</Style>
But it doesn't work this way, and for some reason any child controls start to change alignment, not only images but also text and other controls. The other things I tried just didn't compile. Probably DataTemplate should be used; I'm new to WPF and XAML and I still don't understand it enough and couldn't find what I need yet.

You should use HorizontalContentAlignment to set the content alignment of a button:
<Setter Property="HorizontalContentAlignment" Value="Right" />
Based on your comment below, I can give an example:
<Button Grid.Row="2" Width="150" Height="80">
<DockPanel Height="80" Width="150"><!-- A more complex control here-->
<Image Width="50" Height="50">
<Image.Source>
<BitmapImage DecodePixelWidth="50" UriSource="https://www.gravatar.com/avatar/9eae4ae63d70142e81f0365de42474ae?s=32&d=identicon&r=PG&f=1" />
</Image.Source>
</Image>
</DockPanel>
<Button.Style>
<Style TargetType="Button">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Opacity" Value="0.5" />
</Trigger>
</Style.Triggers>
<Style.Resources>
<Style TargetType="Image"><!-- The style target to the image control only in the button control -->
<Style.Triggers>
<!-- Binding to IsMouseOver of the button-->
<DataTrigger Binding="{Binding IsMouseOver, RelativeSource={RelativeSource AncestorType={x:Type Button}}}" Value="True">
<Setter Property="HorizontalAlignment" Value="Right" />
</DataTrigger>
</Style.Triggers>
</Style>
</Style.Resources>
</Style>
</Button.Style>
</Button>

Using style triggers on a static resource style to change more than properties

I am using Material Design XAML and I am trying to set a togglebutton icon and background color to something else when checked.
RED BOX CODE
<ToggleButton ToolTip="MaterialDesignFlatPrimaryToggleButton"
IsChecked="False"
Grid.Column="2"
Margin="78,58,99,52"
Grid.Row="1">
<Style TargetType="ToggleButton"
BasedOn="{StaticResource MaterialDesignFlatPrimaryToggleButton}">
<Style.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Background" Value="Green" />
</Trigger>
</Style.Triggers>
</Style>
</ToggleButton>
GREEN BOX CODE
<ToggleButton Style="{StaticResource MaterialDesignFlatPrimaryToggleButton}"
ToolTip="MaterialDesignFlatPrimaryToggleButton"
IsChecked="False"
Grid.ColumnSpan="2"
Grid.Column="3"
Margin="205,58,188,52"
Grid.Row="1">
<md:PackIcon Kind="WindowClose"
Foreground="Red"
Height="21"
Width="21"/>
</ToggleButton>
I was thinking I could use the basedon attribute to reserve the style with material design...if possible.
I am trying reserve the style and change the icon and set background color when checked to look like this:
How would I do this?

You are currently setting the Style as the ToggleButton.Content.
You've got to define the Style nested into the ToggleButton.Style property:
<ToggleButton ToolTip="MaterialDesignFlatPrimaryToggleButton"
IsChecked="False"
Grid.Column="2"
Margin="78,58,99,52"
Grid.Row="1">
<ToggleButton.Style>
<Style TargetType="ToggleButton"
BasedOn="{StaticResource MaterialDesignFlatPrimaryToggleButton}">
<Style.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Background" Value="Green" />
<Setter Property="Content">
<Setter.Value>
<md:PackIcon Kind="SmileyHappy" />
</Setter.Value>
</Setter>
</Trigger>
</Style.Triggers>
</Style>
</ToggleButton.Style>
</ToggleButton>

Use an image for a menu option in WPF

I use the following XAML to achieve a menu using radio buttons:
<Grid.Resources>
<Style TargetType="{x:Type RadioButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type RadioButton}">
<TextBlock Text="{TemplateBinding Content}">
<TextBlock.Style>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="Foreground" Value="White" />
<Style.Triggers>
<DataTrigger Binding="{Binding IsChecked, RelativeSource={RelativeSource AncestorType={x:Type RadioButton}}}" Value="True">
<Setter Property="Foreground" Value="Gold" />
</DataTrigger>
<DataTrigger Binding="{Binding IsMouseOver, RelativeSource={RelativeSource AncestorType={x:Type RadioButton}}}" Value="True">
<Setter Property="Foreground" Value="Gold" />
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Grid.Resources>
<StackPanel Margin="25,74,644,78" Background="{x:Null}">
<RadioButton Content="1. Do something." Click="RadioButton1_Click" FontSize="16" Margin="5"/>
<RadioButton Content="2. Do something else." Click="RadioButton2_Click" FontSize="16" Margin="5"/>
</StackPanel>
This works fine but I want to include an image as a menu option instead of text. (The image is for 'Home' and it will have a normal image and a hover over image)
Here is what I want to achieve:
How do I do this?

You can define another style for displaying Radio Button as an Image based on the existing style posted in question, just need slight changes in ControlTemplate's content part. Following is an example of such a Style and the usage :
<StackPanel Orientation="Horizontal" Background="Black">
<StackPanel.Resources>
<Style x:Key="PictSTyle" TargetType="{x:Type RadioButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type RadioButton}">
<Image Width="50" Height="50">
<Image.Style>
<Style TargetType="{x:Type Image}">
<Setter Property="Source" Value="home_default.png" />
<Style.Triggers>
<DataTrigger Binding="{Binding IsMouseOver, RelativeSource={RelativeSource AncestorType={x:Type RadioButton}}}" Value="True">
<Setter Property="Source" Value="home_hovered.png" />
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</StackPanel.Resources>
<RadioButton Margin="5" Style="{StaticResource ResourceKey=PictSTyle}"/>
</StackPanel>

To give a menu item an image:
<MenuItem>
<MenuItem.Icon>
<Image Source=""/>
</MenuItem.Icon>
</MenuItem>
for your trigger just change the MenuItem's icon to the "highlighted one", when the user hovers over the menu item (IsMouseOver), by changing the Icon's image source.

Put an image element as the "Content" property for your radio button
<RadioButton Click=HomRadioButtonClick>
<RadioButton.Content>
<Image Source=""/>
</RadioButton.Content>
</RadioButton>
You'll need some extra logic for the hover behavior, but that should at least get the image in your menu.

Change fontweight on button in WPF treeview

I have a templated treeview that is working just as i want, but i have a context menu which allows for a tier 1 node to be marked as "default".
I have a datatrigger which reacts to a property in the viewmodel, which should change the fontweight to bold just to visually show that this is the default node. But the setter will not change the fontweight on the button no matter what!
However if i change another value, like the foreground color for example, it works just fine, font size also no problem.
Why is this, can anyone explain this? Here is some code if needed:
Trigger:
<HierarchicalDataTemplate ItemsSource="{Binding Children,Mode=TwoWay,NotifyOnSourceUpdated=True}">
<StackPanel Orientation="Horizontal" VerticalAlignment="Top">
<Image x:Name="nodeImg" Source="{Binding Image}" MaxHeight="16" MaxWidth="16"/>
<Button x:Name="nodeButton" Content="{Binding Name}" Command="{Binding Command}" Style="{StaticResource TreeMenuButton}"/>
</StackPanel>
<HierarchicalDataTemplate.Triggers>
<DataTrigger Binding="{Binding RelativeSource={RelativeSource AncestorType=TreeViewItem},Path=IsExpanded}" Value="True">
<Setter TargetName="nodeImg" Property="Source" Value="{Binding ImageExpanded}"></Setter>
</DataTrigger>
<DataTrigger Binding="{Binding IsDefaultConnection}" Value="True">
<Setter TargetName="nodeButton" Property="FontWeight" Value="Bold"></Setter>
</DataTrigger>
</HierarchicalDataTemplate.Triggers>
</HierarchicalDataTemplate>
Default style on button:
<Style x:Key="TreeMenuButton" TargetType="{x:Type Button}">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="OverridesDefaultStyle" Value="true" />
<Setter Property="MinHeight" Value="23" />
<Setter Property="MinWidth" Value="75" />
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Border x:Name="Border"
CornerRadius="0"
BorderThickness="0"
Background="Transparent"
BorderBrush="Transparent">
<ContentPresenter Margin="2"
HorizontalAlignment="Left"
VerticalAlignment="Center"
RecognizesAccessKey="True"/>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

I'd be surprised if your code even built as you can't add a DataTrigger into a UIElement.Triggers collection. Try using a Style instead (this definitely works):
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding IsDefault}" Value="True">
<Setter Property="TextBlock.FontWeight" Value="Bold" />
</DataTrigger>
</Style.Triggers>
</Style>
If by some miracle your DataTemplate does work in a UIElement.Triggers collection, then try using the class name as well as the property name:
<Setter Property="TextBlock.FontWeight" Value="Bold" />

Change Label content with IsMouseOver on checkbox

Hei,
Im creating a button what has a checkbox on top of it. Now when user hovers over the checkbox with a mouse i would like to change the text on the button.
Here's what i have currently:
<Button Grid.Row="1" Margin="0,0,136,12" Name="btnRefresh" Height="28" VerticalAlignment="Bottom" HorizontalAlignment="Right" Width="120" Click="btnRefresh_Click">
<Grid Width="111">
<CheckBox Height="16" HorizontalAlignment="Left" Margin="0,2,0,0" Name="cbAutoRefresh" VerticalContentAlignment="Center">
<CheckBox.Style>
<Style TargetType="{x:Type CheckBox}">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Content" Value="Auto Refresh" />
</Trigger>
</Style.Triggers>
</Style>
</CheckBox.Style>
</CheckBox>
<Label Name="btnLabel" Margin="32,-4,25,-4">Refresh</Label>
</Grid>
</Button>
But like this it changes the content of the checkbox, how can i change the btnLabel content?

Currently you're just modifing the style of the ComboBox, thats why the Trigger just changes the Content of your ComboBox.
To listen to other controls properties in a Trigger, you can use Databinding like so:
<Label Name="btnLabel" Margin="32,-4,25,-4">
<Label.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=comboBoxName, Path=IsMouseOver}" Value="False"
<Setter Property="Content" Value="Refresh"/>
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=comboBoxName, Path=IsMouseOver}" Value="True"
<Setter Property="Content" Value="Auto Refresh"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>