[parkher]

If it has an SD card internally, it should be possible to replace it with a larger one and to expand that 500 MB partition.
But does it?
It is routinely done on various Kobo readers: you make the raw image of the card, then write that image to a larger card and then you get all the original partitions + unused space, then you expand that 500 MB partition. And you still have the original card if something went wrong.
So it would be interesting to open that new Nook and to look inside it.

On Aura HD and other Kobo readers, the original card may be replaced with up to 32 GB card.
You only better use the fastest card you can get, do not replace the original card with a much slower one.