Best option if you want to stay legal is to swap SD Cards.
You will be able to update the EU to the latest version but the US will Stay on the version you bought forever.

quote: Not sure if the following will work, but it's worth trying: US map is much smaller than Europe. Suppose you try to copy the US files into the device's internal memory into the correct folders and sub-folders(!), after having erased the old Europe map) and see if the US map is still acceptable.

This will not work because the Map is unlocked to the volume id of your SD Card.