As far as I can tell, there's no way to mod gems or gold. The game seems to be very heavily server-sided. I have tried using GaneGuardian to mod health during battle, and that causes server incongruity.
The only thing I can confirm this mod does is make your cards level up to max one you use any booster. The effects are seen in battle, but if you go back to the unmodified version, your cards are only wherever level they would have been given the amount of upgrading you did.
Have not yet tried to evolve a card that would otherwise be too low level. If that works and persists even in the unmodified game, then that is a big benefit.
