[Lynne]

There is a difference between the *viewer* of the page being a member of group 31, and the page/post belonging to a member of group 31. Your condition is for the first - the viewer of the page. "if the viewer of the page is in group 31, change the username in this way" either all user names on the page will be changed, or they won't - depending on the group the *viewer* is a member of.

If you are talking about a showthread page, and want the *posters* username to change based on whether the *poster* is in usergroup 31 or not (who cares what the usergroup id of the viewer is), then that is a different condition - you would probably use the variable $user['usergroupid'] in the condition.