This code uninstalls the Microsoft Monitoring agent and re-installs it to a new WorkSpace.

# change your VM Name and it's resource group
$vm = get-azurermvm -VMName YourVMName -ResourceGroupName VMResourceGroup
Remove-AzureRmVMExtension -ResourceGroupName $vm.ResourceGroupName -VMName $vm.Name -Name MicrosoftMonitoringAgent -Force
# put in your new workspaceId & workspaceKey
$workspaceId = "NewWorksSpaceID"
$workspaceKey = "SupaSecretKey"

$PublicSettings = @{"workspaceId" = $workspaceId;"stopOnMultipleConnections" = $false}
$ProtectedSettings = @{"workspaceKey" = $workspaceKey}

Set-AzureRmVMExtension -ExtensionName "MicrosoftMonitoringAgent" -ResourceGroupName $vm.resourcegroupname -VMName $vm.name `
-Publisher "Microsoft.EnterpriseCloud.Monitoring" `
-ExtensionType "MicrosoftMonitoringAgent" `
-TypeHandlerVersion 1.0 `
-Settings $PublicSettings `
-ProtectedSettings $ProtectedSettings `
-Location $vm.Location

Nothing special, just thought I would put it here. Mayby it will help someone?