A player cannot reverse the action once a Joker placing with a natural tile.
Abstract: Symbol tiles also referred to as natural tiles are all tiles except for Flowers and Jokers. Question from a player: What is a symbol tile? Answer from the NMJL: Symbol Tile, “(Also referred to as a Natural tile) –
Discarding a Joker and Naming it the Previously Discarded Tile
When East is playing a Pair Hand, the first discard must be named “Joker,” for obvious reason, there was no previously discarded tile for it to name it after.
Joker exchanges are done by first announcing a Joker exchange is to be made and then by handing the tile to the receiving player.
Jokers exposed before a hand is declared dead are still available for a Joker exchange.
If a player does a Joker exchange and gives him/her mah jongg, it is considered a self-picked mah jongg, and they are paid accordingly.
A player should use Jokers wisely and consider factors such as but not limited to being in the beginning, middle, or end game.
There is no requirement to do a Joker exchange if you have a tile that would allow you to do so. In some cases, a player may choose not to do a Joker exchange if they want to prevent another player from being jokerless or to go for a jokerless hand.
A Joker cannot be used to exchange a symbol tile in an exposure.