Question: I lifted a tile from the wall and then realized that I wanted to call the previously discarded tile. Can I change my mind and call that tile instead?

Answer: Once a player lifts or moves a tile they are committed to taking their pick from the wall. If the tile was merely touched and not moved in any way the player can change their mind and therefore call the previously discarded tile. This ruling is not found in Mah Jongg Made Easy

Source:  National Mah Jongg League Bulletin Q&A 2018