This guide will eliminate the process of HI-APN or any other APN backup apps, strings or scripts. Download the attachment apns-conf.xml on your desktop. This method works from 4.0.4 LF2 to MB1 4.1.2. Phone has to be rooted and bootloader unlocked. Install Root explorer.apk on the phone and place the file apns-conf.xml in system>etc folder. SU will grant permissions. This file contains APNs of the entire GSM networks worldwide, got it from Google code. 2G/3G will work as usual. This mod works on any custom ROM.
4.1.2 and rooting guide:- http://theunlockr.com/2013/04/02/how-to-root-the-verizon-samsung-galaxy-s-iii-running-android-4-1-2/
apns-conf.xml