“By that reasoning, perhaps Christians would also be agnostics, in that if they were to, in the after life come face to face with Set, Moloch, or Dagon (as opposed to St. Peter) they would then have enough information to change their mind.”
Nice attempt at humor there, but in reality one can not be an agnostic and a believer in God at the same time, by definition.
Of course, your point may be that our “God” may not be who we believers think Him to be. In that case, we would still not be agnostic, but just...wrong.
Of course one can be an agnostic, in the sense that you have made a provisional decision, and can change that if the preponderance of evidence changes.