@David Moon,Thanks for posting in Q&A.
For your issue, the short answer is yes.
Based on my research, when you store the wallpaper in Azure BLOB storage account and create a wallpaper policy for device, next time you want to change the wallpaper, you just to change the wallpaper in the Azure BOLB storage account.
Please note that when you replace files with new you must keep the same file names.
Set Desktop And Lock Screen Wallpaper Using Intune (cloudinfra.net)
Non-official, just for reference.
Hope this can help you.
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