Why you would want to do this is totally up to you. It is also just a nice example of using powershell to do xml things 
$doc = New-Object System.Xml.XmlDocument
$doc.Load("C:\Dev\Clarion\ClarionProperties.xml")
$XPath = "/ClarionProperties/Properties[@name='WorkbenchMemento']"
$node = ( $doc | Select-Xml -XPath $XPath ).Node
$node.bounds.value = "1,2,3,4"
$doc.Save("C:\Dev\Clarion\ClarionProperties.xml")