Alterar propriedades de controlos fora Tabcontrol com base no Guia selecionada

Adicionar ambos os controles para o seu layout e mude a sua visibilidade, com base em um datatrigger e o selectedindex do tabcontrol

    <ComboBox>
        <ComboBox.Style>
            <Style TargetType="ComboBox">
                <Setter Property="Visibility" Value="Collapsed"/>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding ElementName=yourTabControl, Path=SelectedIndex}" Value="0">
                        <Setter Property="Visibility" Value="Visible"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </ComboBox.Style>
    </ComboBox>
    <Button>
        <Button.Style>
            <Style TargetType="Button">
                <Setter Property="Visibility" Value="Visible"/>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding ElementName=yourTabControl, Path=SelectedIndex}" Value="1">
                        <Setter Property="Visibility" Value="Collapsed"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Button.Style>
    </Button>