Is it worth risking your system ?. i.e., why do you care ?.
Short answer - the old school way still works, even for the root (for ext). Shrink the filesystem, delete the partition (fdisk say), re-define the partition, good to go.
Don't cock it up - especially aligning the filesystem and the start of the (re-defined) partition. If you're lucky you'll know you got it wrong immediately, else maybe on the next re-boot.
Of course if they insist on XFS you're out of luck anyway.