It depends heavily on how exacting your wording is. It is possible to state "I reject A" in such a way that is equivalent to declaring an acceptance of ~A, because of the Law of the Excluded Middle, which is an accepted axiom of propositional logic (A proposition is always either true or false). However, it is also reasonable to restate the rejection slightly: "I reject this proof of A." This states nothing about the truth or falseness of A, merely that the proof being offered is not sufficient. This is especially important in the handling of axioms. I may believe that Mike is a good dog owner, but not with a sufficient conviction to blindly assume any prepositional logic which may follow from that:
Assume: Mike is a good dog owner
Assume: Good dog owners pick up their dog's poop
Observe: There is dog poop in my back yard
Assume: Mike is the only dog owner with keys to my back yard
Thus: Since Mike is a good dog owner, and good dog owners pick up their dog's poop, Mike would have picked up any poop his dog left in my yard.
Thus: Since no other dog owner has keys to my back yard, my dog must have left the poop
Observe: I did not pick up the dog poop
Thus: I must be a bad dog owner.
You can see why I might like to argue some semantics regarding the validity of these assumptions, but I'd be quick to claim Mike is a good dog owner and good dog owners pick up poop after their dog. Belief is a wiggly thing that way.