Can a sorcerer use 1 sp every round to reroll the damage?

@JKFWEB @JeremyECrawfordOn concentration dmg spells can a sorcerer use 1 sp (empowered spell) every round to reroll the damage? believe you can only use that when initially casting #wotcstaff

— (((Mike Mearls))) (@mikemearls) September 29, 2016