Studies on button text for agreement?

We have an application, that due to factors outside of our control (legal/regulatory), has some very complex rule sets. Because of this, we need users to read a short amount of context on a modal the first time they hit a specific page, about actions they should take.

That being said, we have been discussing the idea of having a button to close the modal with specific text (e.g. "I understand"), in hopes that it will entice to user to read an interpret the text. It seems to work okay in moderated usability testing, but I am attributing some of this to Hawthorne Effect.

Are there any studies on different types of button text and the likelihood that it will influence certain actions, such as reading text before clicking?