European radios tune FM is 1MHz steps, so they are fine in the US where FM tunes in 2MHz steps. AM is tuned in Europe in 9kHz steps while it's 10kHz in the US, they also start somewhere else which makes it to not hit most stations right. In Europe there is also no Stereo on AM.
I have seen so far nowhere that someone successfully changed the radio from EU to US (or vice versa). There is still the hope that sometimes sooner or later it will be possible to flash the EU RNS-E with the US software but this is IMHO more unlikely than getting the US map to work on the EU unit.