Autoprime has made a very excellent utility to backup and restore the EFS partition.
Backup:
Run "Optimus_G_Create_Flashable_EFS.zip" in recovery. It will create flashable zip backup of your EFS in sdcard/EFS_Backup. Copy the same at some safe place.
Restore:
Run the efsbackupflash.zip in your /sdcard/EFS_Backup folder and it will restore the EFS partition.
All experienced members knows but for someone who is unaware, EFS partition holds your MEID, RSN, MIN, etc and messing it up costs a lot.
Download utility from here.
Enjoy