How to switch UserControl on MainWindow from ViewModel

Create an outer viewmodel, that knows if the user is an administrator or a employee, and then have that have a property that returns a viewmodel depending on the user type.

For example, let's say you have these two viewmodels right now;

public class AdministratorViewmodel {
    public string Id {
        get { return Guid.NewGuid().ToString(); }
    }
}

public class EmployeeViewmodel {
    public decimal Salary {
        get { return 100.0m; }
    }
}

And they have their data templates defined as;

<DataTemplate DataType="{x:Type l:AdministratorViewmodel}">
    <DockPanel LastChildFill="True">
        <Label DockPanel.Dock="Top" Content="Administrator"/>
        <Grid DockPanel.Dock="Bottom">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Label Grid.Column="0"  Content="Id:"/>
            <Label Grid.Column="1"  Content="{Binding Path=Id, Mode=OneWay}"/>
        </Grid>
    </DockPanel>
</DataTemplate>
<DataTemplate DataType="{x:Type l:EmployeeViewmodel}">
    <DockPanel LastChildFill="True">
        <Label DockPanel.Dock="Top" Content="Employee"/>
        <Grid DockPanel.Dock="Bottom">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Label Grid.Column="0"  Content="Salary:"/>
            <Label Grid.Column="1"  Content="{Binding Path=Salary, Mode=OneWay}"/>
        </Grid>
    </DockPanel>
</DataTemplate>

Then you can define another viewmodel;

public class MainViewmodel {
    private readonly bool isAdministrator;

    public MainViewmodel(bool isAdministrator) {
        this.isAdministrator = isAdministrator;
    }

    public object Content {
        get { return isAdministrator ? (object)(new AdministratorViewmodel()) :  (object)(new EmployeeViewmodel()); }
    }
}

And set let that have a data template as well;

<Window.Resources>
    <DataTemplate DataType="{x:Type l:MainViewmodel}">
        <DockPanel LastChildFill="True">
            <Label DockPanel.Dock="Top" Content="Some sort of parent container"/>
            <ContentPresenter DockPanel.Dock="Bottom" Content="{Binding Path=Content, Mode=OneWay}"/>
        </DockPanel>
    </DataTemplate>

Then, depending on the user type the MainViewmodel will return either an AdministratorViewmodel or an EmployeeViewmodel instance, and the correct data template will be picked by the content presenter;

Hope this helps,
Fredrik