Eryck, I redid my hornpad a few weeks ago--same design as yours, I expect, with chrome rings around outer and inner edges. I actually used black leather, rather than vinyl, and it came out very well. You need a small screwdriver to bend out the metal tabs that hold the inner trim ring and to pry out the plastic tabs that hold the backing into the outer trim ring. Be careful; it's tough plastic, so the screwdriver can easily slip and couge your fingers.
Not a complicated job, as long as you make certain to line up the star badge carefully before reinserting the inner metal trim ring and folding down the tabs. I also found that with leather, it helped to dampen it with water in order to stretch it evenly over the rubber padding when replacing the chrome rings. Finally, it's a little tricky to make sure your leather (or vinyl) piece has enough extra material on the outer and inner edges to be held in by the chrome rings, but not so much that the trim rings fit too tightly to reinstall onto the plastic backing.
I got a new star badge on eBay cheap--I see them often. The badge is the right size, but the star is larger. An OEM part, but not exactly the same, and perfectionists would not like it. Overall, though, it looks fantastic and a major improvement.
Rick
Dallas TX
1967 250SL, 4-speed