I have loaned my sister one of my Kindles on a long term basis. I do not want to delete all the books on it as she will enjoy them. However, there will be some books I will acquire in the future that I prefer she not see or access.
Is there a way I can add them to only one device (well, actually four) and not add them to the one I loaned to her?
Then, when a Kindle syncs, will it sync across all devices and restore it to the one she has?
The only ways are to, 1. remove that devices access (remove it from your account) then it can't get any additional books, 2. unsync that device from your account 3. don't get any new books you don't want shared.
I know of no other ways, and to be honest, it is easy for numbers 1 and 2 to have a flaw and still allow things to get through.