You won't lose your progress, when you try to access Game Sync it will write the new ds data onto the new card, then a day later you can access the GL like normal.
Oh thank goodness.
Love you Lotads.
Thanks a bunch JCB. I just wanna play on that Reshi/Zek DSi ya know? I should probably register my Nuzlocke copy of White to the GL too so I can go and add the C-Gear Skins to it as well... Because I don't like the default one. xD