Spell trading within a clan
Consider this. The spell factory would have an exta option when selected, much like the clan castle. The button would read trade. When selected it would present the player with the spells currently contained within. The player would then choose one of them and press a button marked trade, which would cause a text box to pop up. The player could then request a specific spell again similar to the manner in which troops are requested. When another player agrees to swap spells and selects the request the spells are switched each moving o it's new owners spell factory. In this way a player may only switch one spell at a time. There should be a recharge time between trades just like between troop requests.