Thank you so much, I'm glad you liked it!
As for the implementation I must say its a little sketchy but I eventually settled to having an 'Entity' class attached to each of the objects, which store a two 'EntityBehaviour' objects - one for the original behaviour and one for whatever it has been switched with. So if coins and bombs were switched, all coins would store a 'CoinBehaviour' and a 'BombBehaviour'. Then the coin could decide which of the behaviours to draw from by switching on an 'EntityType' enum. That's how it retains some of its original behaviour while using some of what it is switched with. I hope that makes sense, it hardly did to me when I was writing it so I'm not sure haha!