Say I want to remove any mapped routes for files with a certain file extension.
RouteTable.Routes.Ignore(\"{root}.hello\");
Works for any
If you're using ASP.NET MVC, use IgnoreRoutes (MVC Extension method)
Routes.IgnoreRoute("{*foo*}", new { foo = @"someregextoignorewhatyouwant"});
If you're using ASP.NET Web Forms, use StopRoutingHandler which implements IRouteHandler.
routes.Add(new Route("*someregextoignorewhatyouwant*", new StopRoutingHandler()));