The hive in setupreg.hiv is use only during install in text mode. After all registry is loading from hive*.inf, so it's useless to modify setupreg.hiv. In graphic mode, there are nothing of setupreg.hiv in registry. The best and easiest solution is to create a hivecst.inf by example (don't forget to add this file into txtsetup.sif and dosnet.inf next to other hive*.inf files), which is call in latest ! If you choose to use a .reg file, the file will loading after the first logon. The advantage of hive*.inf files is they are loading with SYSTEM privileges during install.