How to easily split atlas into smaller atlases?

Long shot but does anyone knows a least painful way to split 2048x2048 atlas into four 1024x1024 and reassign all the sprites again? I could use sprite packer or another tool to do all the rearrangements of the sprites and even the names will stay the same, it is not so much work, but how to find all the objects in the game that uses all of these sprites and reassign them correctly again? When I search for reference in the project it shows everything, so no good. Is there a way to find all the components with missing sprites or something like that?