I found this once commented somewhere but I've forgotten it and I could use it again and can't seem to find it anywhere. It was a really simple command that was part of roll20 itself that just rewrote the last thing you sent in the chatbox into your chatbox again. So if you sent for example /r 6d6>5 and then sent it, you could get it instantly rewritten back into your chat box with this command and have it there to send again.