Board Thread:Dragon City Gameplay Questions & Answers/@comment-10724830-20130627192741/@comment-11469481-20130713013235

they usually not giving you an option to "CANCEL" any activity, but they give you an option to faster the performance by using the gems, yeah "FASTER"! well I'm not sure if you could sell and rebuy it, but base on what other expert have told you above, I think it is impossible.