If I understand correctly you should be able to accomplish it with something like this.
Create a text box object + Create a mouse object
Start of Layout - Set Text "This is the first dialogue"
Mouse On Object(text box) Clicked - Set Text "This is the second dialogue"
From here on you'll require a 2nd specification to be met
Mouse On Object(text box) Clicked +
Object(text box) Compare Text = "This is the second dialogue" - Set Text "This is the third dialogue"