freebsd-update questions

[Pieter Donche]

Ch 24 updating and upgrading freebsd in the handbook says:
The freebsd-update utility can automatically update a GENERIC kernel
only. If a custom kernel is in use, it will have to be rebuilt and 
reinstalled. However, freebsd-update will detect and update the GENERIC
kernel in /boot/GENERIC (if it exists)
It is a good idea to always keep a copy of the GENERIC kernel in 
/boot/GENERIC.

How is this to be understood?
1. e.g. you have a generic kernel  in /boot/kernel and you make a safety
copy in /boot/GENERIC 
# cd /boot/kernel; tar cf - . | (cd /boot/GENERIC; tar xpf -)

when running freebsd-update install, will this update BOTH /boot/kernel
and /boot/GENERIC or only /boot/kernel ?

2. if you have a modified kernel in /boot/kernel (e.g. for disk quota 
enabling) and you run freebsd-update install, then it will not make any 
changes in /boot/kernel. Right ? How does freebsd-update actually detect 
that there is not a generic kernel in /boot/kernel?

If after freebsd-update install, you would do a shutdown -r now (before 
building a new custom kernel, will this be desastreous?