I believe that it was a magic trick, a sleight of hand type of thing. Surely you are not saying it was a demon in the shape of a rod that morphed into a serpent? Are you?
Yes, I believe they performed real miracles, because they turned their rods into snakes, water to blood, and brought frogs upon the land, but could not produce lice. If you ask me, it would be far easier to produce lice than the first three miracles they performed. Lice are tiny, they would be easy to hide. And look at the magician's reaction:
Exo 8:18 And the magicians did so with their enchantments to bring forth lice,
but they could not: so there was lice upon man, and upon beast. 19
Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh's heart was hardened, and he harkened not unto them; as the LORD had said.
Why would these magicians attempt a trick they knew they could not perform? Why would they be shocked? It is obvious to me they fully expected to be able to produce these lice but failed. That makes no sense if it was a sleight of hand trick. And notice they repented and tried to convince Pharaoh to listen to Moses, but he would not listen to his magicians. If they were simply performing tricks, wouldn't they have repented at Moses's first miracle? No, these guys were actually competing with Moses with their magic and doing well.
So, I believe it was obvious they were performing real miracles, sleight of hand with lice would be simple compared to turning rods to snakes, water to blood, and bringing frogs up out of the lakes and rivers.