Rummikub Joker Question
Yes, you can combine sets into new sets. As long as you follow the rules. That is the fun part of the game. 

From Wikipedia:


  Joker substitution:
  A set containing a joker can have tiles added to it, be split apart or have tiles removed from it. The joker can be moved or replaced in any possible way as long as you maintain a set of at least three tiles.