You're supposed to generate a random one, but the only consequence of not doing so is that you won't be able to register your package if someone else already to

You're supposed to generate a random one, but the only consequence of not doing so is that you won't be able to register your package if someone else already took the UUID (which is a pain if you have registered versions in a private registry). That said, "vanity" UUIDs are a bad look, so we'd probably reject them if someone tried that today, but there isn't any actual issue with them.