Well, even outside of Dark Empire, Palpatine had already broken the rule. He had a number of Emperor's Hands, including Mara Jade, and he even trained some of his Sovereign Protectors as Sith, if they proved sufficiently fanatical. I think the point of his attempt at theocracy was, as I said, not merely to rule his Empire through a religious doctrine, but by absorbing every conscious entity into his ego. Even if this would require legions of Dark Side-enhanced minions, this would not pose the same kind of danger that the ancient Sith Lords had to contend with, because by being mere facets of Palpatine's consciousness, they would be equally dependant upon him for their own power. Sort of like his own apotheosis. There's a very good article on that at domuspublica.net.