In today’s Nats/Braves game (5/29/19), the Nat’s pitcher came up in the top of the first. Could the Nats have put in a pinch hitter for the pitcher and still used him in the bottom of the inning?
A pinch hitter is a batter used as a substitute for another batter. A pinch hitter only comes into the game when the batter whose turn he is taking is due to bat. At that time, he is "announced into the game"; the batter which he replaced is out of the game for good.
This clearly states that the batter replaced can not come back into the game, although they may pitch for that team