Out of curiosity, where were you using this? PvP or in Coop?
I've been testing it out in Coop only (won't go into pvp with this) with a friendly account and it seems their coding is really weird.
The other account can't see the changes you make to your card. They also don't run perfectly in sync. The legit account finished the coop without any changes before wave 10 whereas the edited one continued into the 100s. When the two of them went out of sync, any changes made (mana up, new units, etc) took ages to work until it finally said second player disconnected. Their units stay on field, just no changes from them in future.
If I had to guess, the way they coded their game indicates that the tutorial cards are stored on our device and editable whereas any other cards remain on their server and can't be modded.