I'm assuming it is separate, and only needs to be inserted once, is that correct?
Yes.

Also, if I wanted to use this "trick" on more than one message box with a different list of random titles for each, would I just duplicate the code with different variable names, like so?
That's one way, yes.

And finally, is it possible with the above code to use a comma within one of the random title options, for instance if you wanted to use "I don't think so, Scooter!" as one of the options? If so, how would you handle that?
I would read Help for the Split function.