Hi,
Sounds like this is a grey import model, not sure about the sat nav it may be just a matter of replacing the disc, radio should work but only pick up radio 2 on FM as the FM band is different in Japan but you can buy frequency shifters on Fleabay for around a fiver, TV again operates on different frequencies and the sound system is not compatable with UK, having said that it is analogue anyway so will be completely useless when the digital switchover occurs.
It sems a lot of work and money for a short term gain.