Replace service registration in ASP.NET Core built-in DI container?

This is simple using the Replace(IServiceCollection, ServiceDescriptor) method from the ServiceCollectionDescriptorExtensions class.

// IFoo -> FooA
services.AddTransient<IFoo, FooA>();

// Replace
// IFoo -> FooB
var descriptor =
    new ServiceDescriptor(
        typeof(IFoo),
        typeof(FooB),
        ServiceLifetime.Transient);
services.Replace(descriptor);

See also:

• ServiceDescriptor constructors