I found this app on playstore, I think is usefull.
https://play.google.com/store/apps/details?id=com.nthung.lgbackupimei
It can backup imei from lg optimus g to lg g3, only need root.
https://play.google.com/store/apps/details?id=com.nthung.lgbackupimei
It can backup imei from lg optimus g to lg g3, only need root.