I'd call the box office to find out about how to do the LED messages. For the Vegas show, that's what I used to do, call the box office and ask, then they'll give you the number to call for it. Do it well in advance of your show date, though!! It's great fun to surprise a first-timer to the show with a message. They even gave me my own message one time when I'd called for someone else!
The meet & greet after, in the lobby, is for everyone. The Blue Man guys will come out and take pictures with you and sign the program, if you have one. Mind you, the "signatures" are quite unique (and you won't be able to close your program until they're dry).
Just did the show at Universal and enjoyed it, although I think the crowd is better in Vegas.