We implemented weapon/armor fusion system to be able to implement custom items and not ruin the balance. That system gives you another weapon or armor and a bonus skill that gives you some bonus stats, but only for a limited period of time, so you must know when to use it.
We will modify this system in the future so you can select how the items you receive will look like from server's custom items.
For the balancing matters we already implemented a system that can alter the damage output and intake of every class (that includes summons for summoners). We just need feedback from players to see which class is Overpowered and which class is Underpowered.
For the method you obtain the items needed for class change as I said before we didn't think of anything yet so your opinions are welcomed. In beta class change will be free.