Reboot with kexec without making it default and vice versa

Upon installing kexec-tools, on Ubuntu at least, I am asked if I want to use kexec to handle all invocations of reboot. I don't, but there are some occasions that I do want graceful termination of running processes and unmounting of filesystems and then execution of kexec to reboot the system. How can this be achieved? And suppose that I someone has made rebooting with kexec the default. How would someone invoke a normal reboot in that case? Answers should not be restricted to systemd.