I also think this half changed card is a nice visual moment. I actually do similar effect (except, don't change whole deck in the end). It's nice to let them touch the card before you change it complitly. You can actually pick it up, scratch it a little bit, let them touch it. Just make sure you don't expose the other side. And then go to complite change. This usually makes the reaction even bigger. Hope it helps
Nice effect!