If that is a metallic decal like the air cleaner, I've had good luck with heat from the backside and a piece of good dental floss. The floss will cut right through the foam and adhesive and get it off without damage. That was a trick I learned with automotive emblems.
Going back on is the same. Any auto paint store and even some regular auto parts stores carry the good 3M auto trim foam tape. I've even seen it in the Walmart automotive section. Carefully pick the old foam off the emblem, reline it with fresh tape and when you're ready to install, peel the backing and press in place.
