Ok but the thing is whenever I switch to another cards, I have to set up againYes, you can use infinite amount of micro cards.
You can even transfer save files between cards.
Ok, usually I press Blue button after finishing game. Then turn off. But next time, I still have to set up again although it doesn't lose save games. One thing that I really concern is after changing micro cards Cubic Ninja still need to install againbefore removing the Sky3ds from your console, change the active game. this will save your savegame back to the SD card.