If you reainstall manually grub-common and do apt -f install you manage to downgrade.
However there is a logical bug in installation as grub2-common should be removed/downgraded before grub-common is installed...
-- Eric Valette
as the file in grub2-common during the transition from 2.12 to 2.14
migrated from grub-common to grub2-common, when removing files it
remove the grub-common just installed files.
