No; P=1 has a very specific, slightly absurd technical meaning. If you believe any statement has a probability of exactly 1 or 0, and you obey the rules of probabilistic reasoning, then no finite amount of evidence can ever change your mind. This is why some argue that 0 and 1 should not be considered probabilities at all; they represent states of knowledge that require infinite evidence (and in some alternative representations of probability, are actually infinities).

I am an atheist, but not with P=1. Saying that God does not exist with P=1 would mean that I should maintain that belief even if the stars suddenly rearranged themselves into English text that said otherwise, and that would be more than sufficient to change my mind.