De acordo com a documentação do RHEL, você não pode:
XFS quotas are not a remountable option. The -o quota option must be specified on the initial mount for quotas to be in effect.
Também tentei alterar uma cota de usuário (teste) usando:
xfs_quota -x /home
xfs_quota> report -hu
User quota on /home (/dev/mapper/cl_backup--server-home)
Blocks
User ID Used Soft Hard Warn/Grace
---------- ---------------------------------
root 0 0 0 00 [------]
test 11,4G 9G 10G 00 [-none-]
xfs_quota> limit bsoft=30g bhard=32g test
xfs_quota> report -hu
User quota on /home (/dev/mapper/cl_backup--server-home)
Blocks
User ID Used Soft Hard Warn/Grace
---------- ---------------------------------
root 0 0 0 00 [------]
test 11,4G 30G 32G 00 [------]
xfs_quota> q