I want to reinstall OS X on my Mac without having to re-download my (very large) Photos library. Ideally, I would simply copy the .photoslibrary file from my system disk to an external, reinstall OS X, copy it back over to my system disk, and voila: done. But I suspect my iCloud settings will get upset. Could somebody advise on how I do this? I frequently reinstall OS X on my Mac but haven't done so since getting the Photos library (which I'm very happy with). And, before anybody suggests it, I don't use Time Machine and nor do I want to.