Taking off your back bumper and modding your CK with a smooth rollpan can add tremendous value to the look of your truck.
GMC Silverados are known to look fantastic with rear rollpans installed instead of the stock bumper so you should look into replacing your bumper soon.
A lot of states didn't require bumpers on trucks until recently, so see if your CK truck is one. If so, you should be fine.
Each states laws are different where bumpers are concerned so you should check on yours. You'll find that usually you will be left alone unless you are causing trouble...or the local cops are looking for something to do ;)
Once you've lost that bumper, you will also want to shave those taillights and maybe even headlights.
Custom taillights cut right into your tailgate can really set your truck apart. When replacing the taillights be sure to have backup lights as well.