Rules when using a Joker
Note: all quotes taken from this set of rules.

Yes, you can replace the Joker with either of the missing 10s (in this case, a blue 10)


  In the case of group consisting of two equal tiles and a joker, the joker can be replaced by a matching tile of either of the missing colors.


Yes, you can use the retrieved joker as any tile; you are free to change the color and/or rank it represents.


  a player who has in hand the tile which is represented by a joker on the table, the player can substitute the real tile for the joker and then re-use the joker in some combination on the table.


And note: this is "yes" only if you've already set out your initial meld. You can't retrieve a joker before putting down your first meld.


  The first meld made by each player must consist of one or more combinations formed entirely from that player's hand