Captured template deployment only works the first time.

I've generalized and captured a vm using the azure cli, and then I try to deploy the template using the cli command azure group deployment create -f template.json -e parameter.json resourcegrouplocation newvmnew

The first time I do this a new vm is created fine, but the second time I get errors.  If I change nothing in the template.json file I get the error that the disk blob is already in use; that makes sense at least.

However, I have also tried changing the osDisk vhd uri value as mentioned in Virtual Machines Linux Capture Image and then the error I get is"Changing property 'osDisk.vhd.uri' is not allowed."

Is there something else that I need to do to allow multiple vms to be created from the same captured template file?

Thanks