What is the difference between Nietzsche's idea of going "beyond good and evil" and just being immoral/amoral?

Answer 1

The difference between an existentialist and a nihilist in this case is that only the latter believes that moral distinctions cannot exist. Where they both agree is in the idea that there is no inherently correct pre-existing morality.

So to directly answer your question, to Nietzsche someone who is 'beyond good and evil' doesn't have NO moral code... he just has one that is self-defined and knows it. Instead of swallowing dogmatic so-called-truths handed to him by others, the ubermensch creates and lives his own truth.