Are you sure you are using 4.7?
This is indeed in 4.7
require "languages/$pplang/pp-inc.php";
to give you a further hint that line is line 50 of pp-inc.php
and the printheader function is indeed from 4.7 you are replacing the entire printheader function which as always is the staple of this hack.
As far as the stylesheet in admin section that is not seen by anybody and I considered useless from this hacks standpoint.
You can find the stylesheet call in adm-inc.php and fill out the full path to a stylesheet you want to use but has no value on the workings of the hack which is to change the stylesheet based on a user's stylesheet which is all front end stuff.