I just purchased "3dcarbon" lower side scoops. The installation instructions say to apply the "adhesion promoter" to the painted surface of the body before applying the scoop to the body.
Is this really necessary. Could this chemical cause a discolor of paint if later you decide to remove them.

 

Possible... what exactly is it?
You will need to apply something to remove all wax. Other wise they will blow off the first time you go over 60. There is clearcoat over your paint, so I don't think it's going to harm the paint just by using it.
What's more likely is that having the scoops on the car for a long time might cause a difference in paint color due to fading. If you remove them within a year you probably won't notice a big diff, but after 3+ years, if your car is in the sun a lot, parked outdoors, etc... possible

 

I have used alcohol prep pads, 3M adhesive remover, or rubbing alcohol. You want to ensure that there is no wax built up on the surface. These items will no harm the paint.