foreach (var instance in instances)
            {
                builder.RegisterInstance(instance).Keyed<IInstance>(InstanceType.A);
            }
IContainer container = builder.Build();
DependencyResolver.SetResolver(new AutofacDependencyResolver(container));

//...dispose old instances, obtain new instances

var builder = new ContainerBuilder();
 foreach (var c in _componentContext.ComponentRegistry.Registrations)
            {
                builder.RegisterComponent(c);
            }
 foreach (var instance in newInstances)
            {
                builder.RegisterInstance(instance).Keyed<IInstance>(InstanceType.A);
            }
builder.Update(_componentContext.ComponentRegistry);

class Program
{
    static void Main(string[] args)
    {
        ContainerBuilder builder = new ContainerBuilder();
        builder.RegisterInstance(new FooProvider(new Foo("a")))
               .As<FooProvider>();
        builder.Register(c => c.Resolve<FooProvider>().Value)
               .ExternallyOwned()
               .Keyed<Foo>(1);

        IContainer container = builder.Build();
        using (ILifetimeScope scope = container.BeginLifetimeScope())
        {
            Do(scope);
        }

        using (ILifetimeScope scope = container.BeginLifetimeScope())
        {
            IComponentContext context = scope.Resolve<IComponentContext>();
            container.Resolve<FooProvider>().Value = new Foo("b");
            Do(scope);
        }

        using (ILifetimeScope scope = container.BeginLifetimeScope())
        {
            Do(scope);
        }
    }

    static void Do(ILifetimeScope scope)
    {
        IIndex<Int32, Foo> index = scope.Resolve<IIndex<Int32, Foo>>();
        Foo foo = index[1];
        Console.WriteLine(foo.Value);
    }
}

public class FooProvider
{
    public FooProvider(Foo value)
    {
        this._value = value;
    }

    private Foo _value;
    public Foo Value
    {
        get
        {
            return this._value;
        }
        set
        {
            this._value = value;
        }
    }
}
public class Foo
{
    public Foo(String value)
    {
        this._value = value;
    }

    private readonly String _value;
    public String Value
    {
        get
        {
            return this._value;
        }
    }
}