Grub already can search by uuid or label (via "search --fsuuid" and
"search --label", respectively).  IF you specify an uuid or label
in your operating-system configuration it will use that.

The only part missing is: The Guix installer's config generator should
find out the uuids and print those instead of the /dev nodes.

If nothing else, we can just use blkid to find out which is which.

For example: blkid -d -s UUID -o value /dev/sda1

But T G-R is right, Guix already does what is required at other places.

Care has to be taken that parted also uses GUIDs for GPT partition TYPES
and also for partitions as such (not their contents).  Those are something
else.