you won't void the warranty - there's no sticker or anything to tell if its been opened. i took out the old card, and copied the contents on to a new class 10. it's really easy to do, just a couple of screws.
if you are returning it, just put the old SD card back in.
some of the tpcasts did come with class 10 cards as stock, it just depends on what tpcast had available.
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