Question

Is it possible to delete and create a new game sync ID without restart the game ?

Answer 1

Once you start your game, the ID is already made. As far as I know, there's no way of changing/resetting it.

Comments

does that mean if i remove the game card registered , i will not be able to use pokemon GL anymore , or re register with my old game sync code too ?

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Every time you start a new game, the code gets generated.  You can re-register the new code, but you would have to delete the old code from Pokemon-GL.