I think you need to take the time to listen to the recording of @shadowpub's witness chat this past Saturday ... https://steemit.com/witness-category/@shadowspub/another-successful-witness-chat There is discussion on there how changes get made on the blockchain.

You'll learn a lot more about witnesses and what they do listening to the other two chats as well ... you can find the recordings through this link ... https://steemit.com/witness/@shadowspub/everyone-is-welcome-to-the-witness-chat-on-saturday-in-the-steemit-ramble-discord