I can only think of one player that this happened to, Carlos Delgado
but again, a players batting ability rarely has anything to do with what position they play. i mean they were scouted, drafted, and groomed to play that position. say for instance your second baseman becomes your leading HR hitter, a team isn't going to say, oh, thats not a power hitting position, so we're going to move you.
try telling Cal Ripkin or Mike Piazza, who are in the top 50 of all time HR leaders, they aren't going to play SS or catcher cause they hit too many HR's