Mr. Wallet, on his server, has modded my Brick Messages to be a lot better, not chatspamming when sitting on the brick and allowing you to either chat normally after hitting the brick or use !Message to set the message once. I think it allowed you to change the message after, too.
If you're looking for a good Brick Message mod I think his is a good way to do it. If not you could always try GMP's change at the back of my topic or do what ·•{ Awoken } said and attempt coding one yourself. I'm not copyrighting the idea, it was technically Ephialtes or whoever made the Brick Messages in Return to Blockland who should 'own' it.
