InfoPath Dev

 I seem to have all the pieces but this is the first time i have built this type of control, so I am not familiar with the username function.  How do I set the rule to make it visible to just those users, as I am trying to accomplish this i only seem to be able to hide the button not make it visible to the correct users.?

I currently have a form that is for a multistage approval  process upon the last approval the form is opened in read only from that point forward.  What has been requested is a way that an admin/super user can go back into the form and edit it.  If at all possible i would like to just add a button that is controlled either by a list ...