Adding new entry to GRUB for another OS on the third drive and turning system back to work?

[znavko]

Hello, Guix help!
Please, look through my short booyloader configuration, will it break my system?
(operating-system (host-name "antelope") (timezone "Europe/Moscow") (locale 
"en_US.utf8")
 (bootloader
 (bootloader-configuration (bootloader grub-efi-bootloader)
 (target "/boot/efi")
 (menu-entries (menu-entry
 (label "Ubuntu")
 (linux "(hd2,gpt3)/boot/vmlinuz")
 (linux-arguments '("root=/dev/sdc3"))
 (initrd "(hd2,gpt3)/boot/initrd.img")))))
 (file-systems (cons*
 (file-system (device "/dev/sda1") (mount-point "/boot/efi") (type "vfat"))
 (file-system (device "/dev/sda2") (mount-point "/") (type "ext4"))
 %base-file-systems))
...
I just learned how to use GRUB for booting to another OS placed on another SSD 
in my PC.
And now I want to add another OS to GRUB's configuration, that is holding by 
Guix.

Could you say, is this config workable?

And also if something goes wrong in my experiments, how to get back to previous 
workable Grub configuration?
Can I do it with Guix usb stick? Which steps to do for reconfigure my system 
and "cow-store" from usb stick?