subscribed! This is a great writeup. I've been thinking about doing this to the V1 on my e90 for a while now. Do you have any more pictures of how you ran the cables and connected them to the button and the V1? I'm not an electrician by any stretch, so this would be a starting from ground zero project for me as well.
I'm also curious as to how the wheel function buttons are backlit. Is the clear part that lets light through the shape of the icon displayed or is the entire button clear and then overlayed with black to produce the shape shown (up/down arrows, telephone, etc).
It would be a nice touch to change the logo on the button you reprogram to have the V1 logo on it.