So I have a Magellan GPS unit that came shipped with a 4gb MicroSD card with 1:50 000 Ordnance Survey maps of the UK on it. The maps are great, but take up all of the space on the memory card bar about 600mb.

I'd like to swap the MicroSD card for something higher capacity so that I can store other maps and photos etc on it. The problem is it appears that the maps are hard-coded to the SD serial number.

Is it possible to change this, or is it hard-coded into the card?

I'm pretty sure you cannot modify the serial number of devices like that, be they flash, USB, etc. You'll probably find there is some way to change the serial number assigned to the maps somewhere, do they have a users forum somewhere that you could check out?

Yeah, problem is the maps are seriously encrypted, the serial number reference is buried in the jargon you'd get if you opened a jpg in notepad. It was wishful thinking that it might just be easier to switch serial numbers.

I don't know specifically what software yours is using, but maybe take a peek at some of these and see if they are of any use to you (just a few links I picked up googling about it):

http://www.tritonforum.com/forum/viewtopic.php?f=27&t=2317

http://www.playcircuit.com/map-switching-sportrak-pro-43010.html

http://www.fixya.com/support/t621285-topo_map_purchase_magellan_gps