Can you use the same data in your 3DS from a game and use a different cartridge?
No, if you own the retail/cartridge copy of a game, its data
(excluding any generated "extra data", such as StreetPass) will be
stored to that cartridge, and any console it is played on will have
access to the save data that is currently available. I don't
believe it's possible to transfer/copy data from one cartridge to
another without problems.