How do I replace an iCloud photo library with an updated one?

For years I've had a cluster** of photo's on multiple hard drives and a computer or two... I've finally gotten around to consolidating and removing duplicates etc from my Photo's library and externals. I have a new Mac mini that I've loaded and sorted through (for the most part). My massive (25000+)iCloud photo library was linked to my old iMac. (I've backed up everything on different drives in case things go bad) I've turned off wifi so that my iMac can no longer "speak" to the cloud. I've turned off iCloud photo's on both my devices (iPhone and iPad) The photo apps on them are empty now. SOoooooo......the question is: If I now link my new computer with its new Photo's library to iCloud photos, will it replace my previous library? I hope that made sense.