Creating and mounting a disk using cloud-init after a server is installed

Is it actually possible to run cloud-init to create a disk after the VM itself has been created?

I have a VM created on a VMware platform. Currently cloud-init is not enabled on the GUI for creating VMs. I am trying to attach a newly-created disk. This appears as sdb but is not formatted or mounted.

I can create the disk manually using:

fdisk /dev/sdb
mkfs -t ext4 /dev/sdb1
mount /dev/sdb1 /data

but obviously this leaves me with a non-reproducible installation, and I'd rather this stuff was defined in the cloud-init file.

I have tried including this in the cloud-init file:

# Disk
resize_rootfs: false

disk_setup:
#  /dev/sda:
#    table_type: 'mbr'
#    layout: true
#    overwrite: false
  /dev/sdb:
    table_type: 'mbr'
    layout: true
    overwrite: false

fs_setup:
#  - label: root_fs
#    filesystem: 'ext4'
#    device: /dev/sda
#    partition: auto
#    overwrite: false
  - label: data1
    filesystem: 'ext4'
    device: /dev/sdb
    partition: auto
    overwrite: false

mounts:
  - ['/dev/sdb1', '/data']

then running it using

sudo DI_LOG=stderr /usr/lib/cloud-init/ds-identify --force
sudo cloud-init clean --logs
sudo cloud-init init --local
sudo cloud-init init

which I understand will run cloud-init as if it were instantiated upon first boot install. I have confirmed the file is being run as I've tested this by adding a write_files section to write a test file successfully.

However, this disk creation seems not to take effect.

(Do I actually need to include the pre-existing disk, or is it enough to show only additions in disk_setup and fs_setup?)