That makes sense that Devon would switch with Rockslide, and sort of lurk there inside Rockslide, and switch again to whomever shows up to graffiti Rockslide. Since Rockslide, who is more or less catatonic, would be in Devon's real body, he could use Rockslide's body to just go stash it in some bushes or something and then go stand back where Rockslide usually stands and wait for victims to come to him...
Although exactly why Devon is doing this is beyond me. I could see him being popular with people who want to do some switch-a-roo shenanigans for fun, like a pair of lovers who want to swap into each others bodies for a time, to see how the other half lives, or someone swapping temporarily into the body of an aquatic mutant or a flier, to enjoy those unique experiences.