With Rian Johnson taking over directing duties from J.J. Abrams, he’s entitled to make some slight changes here and there, especially since it looks like we’ll be seeing more of Kylo Ren’s face in The Last Jedi judging by his destroyed helmet in the trailer.
It’s also poetic that Kylo Ren’s scar has been moved to above his eye, since his grandfather, Anakin Skywalker was scarred in almost the exact same place during The Clone Wars.
While this does present a slight continuity error, the fact is that Kylo Ren’s scar is only seen for a couple seconds in The Force Awakens, because soon after, he was separated from Rey, and they both hightailed it off Starkiller Base as the planet was collapsing.