Thank you for some of your answers.

I saw this video @ youtube: YouTube - modding the k800i

So you say, the basic OS of the phone is untouched and so anything will work after a correct debranding?Good to know.

What do I have to do, to make my phone look like this in the video? Are there performance or any other issues with debranded phones?

An other questions about the phone: Is the joystick as bad as on the K750i? (Doesn't react/is defact)