Science partakes of both inductive and deductive reasoning. The theory of intelligent design works well in both directions, and it covers every conceivable situation in the known universe. If you think you can engage science without any a priori method then you may indeed be a candidate for belief in the spaghetti monster.
This does not mean it is not a posteriori.
"The theory of intelligent design works well in both directions, and it covers every conceivable situation in the known universe."
It therefore is completely worthless. It explains nothing in particular.
"If you think you can engage science without any a priori method then you may indeed be a candidate for belief in the spaghetti monster."
If you think that you can have a scientific theory that can never be falsified or tested, because, as you said, "...it covers every conceivable situation in the known universe.", then you haven't a clue what science is.