GMC Wiring/Lighting Help

I have a 2014 GMC Sierra and need to get advice to see if what I want is possible. There are a lot of great lighting features on this truck, under bed rail lights, under mirror lights, interior lights, cargo light, etc... What I want is to add a few backup lights and a switch to turn them all on at once. Is this even possible? My main frustration is the rear cargo light has a direct switch, but it will not come on unless the truck is in park. This makes it difficult to check loads while going down the road at night. I think it would be great to get to the lease and while unloading, be able to turn all exterior lights on except for headlights. Any help is appreciated.

winner, I work for a GM dealer pm me as much info on what you would like to do and I will see if I can send you some wiring diagrams that should help if I can

I think I have the info you need. not sure if I can send them electronically will try to figure it out later today

PM Sent! Thanks for your help. If anyone else needs the info, just let me know.