ok, I've tried that.. I put original 9.510 on a clean SD card, then put a patched 9.510 installation on top. I've set it to 720 emulation mode just to rule out any issues there...

When I connect it up to TTHome, it says I have a GO 720 (that's in the ttgo.bif). I now get a new button which says "get free map corrections from mapshare", but when I click it, I get a message "TomTom Map Share is not supported for your device or for the map you are using". It's the same map that when I put on internal storage it was more than happy enough to update. hmm...