Dynamicaly modify an unattended.xml in powershell to add a partition and format it

Hi Guys,

I have an unattended.xml file which setup parse well. I would like to dynamicaly modify it before launching setup according the hardware detected.

For instance, I would like to add a partition and format it if the disk is big enough. I found how to detect disk size in powershell, but I can't find a way to modify the xml file

So, I would like to add

 <CreatePartition wcm:action="add">
    <Order>3</Order>
    <Type>Primary</Type>
    <Extend>true</Extend>
</CreatePartition>

I made some tries without success.

$Xml contains the xml file.

To create the data, I found two ways :

Long :
$NewPartition = $Xml.CreateElement("CreatePartition")
$Order = $Xml.CreateElement("Order")
$NewPartition.AppendChild($Order)
$OrderValue = $Xml.CreateTextNode("3")
$Order.AppendChild($OrderValue)
<...>
Or :
$NewPartition  = [xml] '<CreatePartition><Order>3</Order><Type>Primary</Type><Extend>true</Extend></CreatePartition>'

Then, how to add $NewPartition to the right place in $Xml ?

$Xml.unattend.settings[1].component[1].DiskConfiguration.disk.CreatePartitions.AppendChild($NewPartition)

Could someone give me a correct code ?

Thank you very much

ML

Here are the content of my unattended.

<component name="Microsoft-Windows-Setup" processorArchitecture="amd64" publicKeyToken="31bf3856ad364e35" language="neutral" versionScope="nonSxS" xmlns:wcm="http://schemas.microsoft.com/WMIConfig/2002/State" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
            <DiskConfiguration>
                <Disk wcm:action="add">
                    <CreatePartitions>
                        <CreatePartition wcm:action="add">
                            <Order>1</Order>
                            <Size>350</Size>
                            <Type>Primary</Type>
                        </CreatePartition>
                        <CreatePartition wcm:action="add">
                            <Order>2</Order>
                            <Type>Primary</Type>
                            <Extend>true</Extend>
                        </CreatePartition>

==> Add here !

                    </CreatePartitions>
                    <ModifyPartitions>
                        <ModifyPartition wcm:action="add">
                            <Order>1</Order>
                            <PartitionID>1</PartitionID>
                            <Label>System</Label>
                            <Format>NTFS</Format>
                            <Active>true</Active>
                        </ModifyPartition>
                        <ModifyPartition wcm:action="add">
                            <Order>2</Order>
                            <PartitionID>2</PartitionID>
                            <Format>NTFS</Format>
                            <Label>Windows</Label>
                        </ModifyPartition>
                    </ModifyPartitions>
                    <DiskID>0</DiskID>
                    <WillWipeDisk>true</WillWipeDisk>
                </Disk>

ML