Well, sure you can do this wherever you like with the right programming. Consider this:
If you remove x/y.aspx, IIS won't find it and will deliver a 404. However, if you set your application to have a custom 404 error page, then this custom page could check the URL that is being requested against some list. That list should have the old to new page mapping so you can then redirect the user to the new page. If there isn't a mapped page then you can deliver a true page not found error.