I tried to learn how to do this from other users on Youtube, and I only found one person who went crazy and destroyed the original Replace your Mercedes Benz key fob casing without having to pay hundreds for a new key from the dealer, not to mention the hassle of having to reprogram the keys. I went on eBay, bought a new fob casing for ~$20 and replaced the entire thing in few minutes, while preserving the original.

I hope this video helped