That I'm not sure about. It's your disc and as long as you do not duplicate it to sell, you can do as you please. There's certainly nothing illegal about integrating a custom POI as far as I'm aware!Point taken!
Unfortunately none of this stuff is strictly legal. Hacking the code and making a duplicate disc even for personal use are both illegal acts in Europe and the US.
However if BMW did decide to prosecute for hacking their software/discs they might be lenient if you had the original disc!