The Navigation Bar is hard to change. I recommend you to create you own.
Create you own buttons and then use
myFrame.NavigationService.GoBack()
myFrame.NavigationService.GoForward()
Example:
Private Sub PreviousPageCommand_Executed(ByVal sender As Object, _
ByVal e As ExecutedRoutedEventArgs)
MainFrame.NavigationService.GoBack()
End Sub
Private Sub PreviousPageCommand_CanExecute(ByVal sender As Object, _
ByVal e As CanExecuteRoutedEventArgs)
If Not MainFrame Is Nothing Then
e.CanExecute = MainFrame.NavigationService.CanGoBack
Else
e.CanExecute = False
End If
End Sub
Private Sub NextPageCommand_Executed(ByVal sender As Object, _
ByVal e As ExecutedRoutedEventArgs)
MainFrame.NavigationService.GoForward()
End Sub
Private Sub NextPageCommand_CanExecute(ByVal sender As Object, _
ByVal e As CanExecuteRoutedEventArgs)
If Not MainFrame Is Nothing Then
e.CanExecute = MainFrame.NavigationService.CanGoForward
Else
e.CanExecute = False
End If
End Sub