Enabling or disabling validation upon context - wpf

Question

Introduction
I have two TextBox in my view, each binded to some properties in my view-model (Property1, Property2).
TextBox are alternatively enabled upon some boolean, and properties, are validated using IDataErrorInfo in the view-model + some styling in the view.
Problem
I would like to disable validation style when items are disabled.
NB1: Currently, solution I found is to change validation scheme directly in the view-model, but this requires to notify for property changes in order to force the view to re-read IDataErrorInfo (while properties haven't really changed, only selector ...)
NB2: My problem is really close to this one, but the description and the solutions are far too complex for me to really get the point.
Pseudo-Code
<UserControl
<UserControl.Resources>
<Style TargetType="{x:Type Control}" x:Key="ControlValidationStyle">
...
</Style>
</UserControl.Resources>
...
<TextBox
Text="{Binding Property1,
ValidatesOnDataErrors=True,
UpdateSourceTrigger=PropertyChanged}"
IsEnabled="{Binding IsMode1}"
Style="{StaticResource ControlValidationStyle}"
/>
<TextBox
Text="{Binding Property2,
ValidatesOnDataErrors=True,
UpdateSourceTrigger=PropertyChanged}"
IsEnabled="{Binding IsMode1,
Converter={StaticResource BoolInverse}}"
Style="{StaticResource ControlValidationStyle}"
/>
</UserControl>
ControlValidationStyle
<Style TargetType="{x:Type Control}" x:Key="ControlValidationStyle">
<Style.Resources>
<Style TargetType="ToolTip">
<Setter Property="Background" Value="Tomato" />
<Setter Property="BorderBrush" Value="Red" />
<Setter Property="BorderThickness" Value="2" />
<Setter Property="Foreground" Value="white" />
</Style>
</Style.Resources>
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors)[0].ErrorContent}" />
<Setter Property="Background" Value="Bisque"/>
<Setter Property="BorderBrush" Value="Red" />
<Setter Property="BorderThickness" Value="2" />
<Setter Property="Foreground" Value="Red" />
</Trigger>
</Style.Triggers>
</Style>

Answer 1

Why wont you use MultiTrigger instead of Trigger:
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="Validation.HasError" Value="true" />
<Condition Property="IsEnabled" Value="true" />
</MultiTrigger.Conditions>
<Setter .../>
</MultiTrigger>