Question New head unit and existing DVD

[OKstate]

I know this is similiar question to what has been asked but couldnt find any answers. So heres one for ya audio guys:

I have factory overhead dvd player. Looking to replace jbl head unit with pioneer double din dvd. Will this mess up the factory overhead dvd?

I have gone a couple places and they all say, we can charge you 100 bucks to try it out. I find that a little rediculous that they have been doing it for so long and dont know something like that.

Anyone have ideas or experience? thank ya