Thanks for reaching out to Microsoft Q & A Platform .
Regarding your question , Azure doesn't support the OS Type change osDisk.osType .
Also you can make copies of OS disk and use them to swap with available backups in the DR situations
Ref:
https://azure.microsoft.com/en-us/blog/os-disk-swap-managed-disks/
https://learn.microsoft.com/en-us/azure/virtual-machines/snapshot-copy-managed-disk?tabs=portal
Thanks,
Pradeep
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