They can keep the basic events that have happened in the DCEU, change the tone of the films, wrap up any lingering narrative threads, and the films could swing in a different direction without having to dump everything that came before.
All in all, the problem with the films hasn't been the actors, the costumes, or even the basic plots. I mean, Superman shows up to save earth from aliens. Some people dont like him. Batman has gone off the rails and is manipulated into fighting him. Clark dies fighting Doomsday. Amanda Waller recruits the Squad. Batman assembles the League to fight an evil New God and collect some Mother Boxes.
Nothing wrong with any of that, but the execution is what has left people cold. So change the execution and push things in a more positive direction and you're good to go.