Activity Guides - Modify Buttons on Message pop up?

Hello,

I'm taking my first stab at creating a custom Activity Guide for one of our business processes. Along the way I've added custom buttons to various Action Items that provide simple informational help. Each one just calls a message from the Message Catalog. Is there a way to modify the window that appears to render just an "OK" button versus the default Yes/No options?

I've attached an example of what I'm referring to. The message in this instance is supposed to just instruct the user to contact the person needed, so I don't need the Yes/No options, an "OK" option would be preferable.