For future referance, InfoPop does not support modifying stock code; in fact, by modifying your code you're voiding your warrenty. With that out of the way,
UBBDev is a large site for modifications.
This issue in particular is an easy one (in 6.7 at least) as it doesn't involve modifying a thing, login to your control panel, click "member management", browse to the member you wish to edit, click the "Fields" tab and change "User Custom Title" to what you'd like to display.