I'd like to dual bool W10 with 7. Both OS's are already install, on different disks. Is there any way to add dual booting without an OS reinstall? Everything I've googled says to set it up during OS setup and has no suggestions how to do it later. Currently I do it by going into the BIOS and selecting the drive I want to boot from.

Also, I'd like my files available on both OS's, but I also want access restricted in case anyone gets into the network from the internet. For example I'd like my user on both OS's to have full access to my personal files, but I don't want other users or anonymous users to have access. I think I can do this by just giving "everyone" access temporarily then adding permissions in the new OS. Sound right?