I don't know if it's possible to load a new kernel without rebooting...
But I think people who doesn't want to reboot because feared of a bad reboot, loose SSH or anything else... If OS's teams are updating a system for security, I prefer a bad reboot (backups are done before!) than a system with a lot of security holes, sick of botnets or sending spams every seconds, a Tor relay controlled by bad hands... :s
On other servers (debian/raspbian) I usually use "apticron", it sends everyday mails to root or another admin@domain.com, with summary about updates available for the host.
but I still need to manually reboot to apply kernel upgrades.