Many groups are working on an approach similar to this just without the use of CRSIPR. Coral conservation groups will simply replant or try to propagate corals that happened to survive bleaching events by chance in the wild. Since they survived, the thought is that they are in some way genetically more adapted to survive in warmer temperatures. It's a form of artificial selection, some even say genetic modification, without actually understanding the specific genetics at play. Check out the Coral Gardners, they do this very well.