Here is a sample printing properties for a vdir. You can filter on vdir name and then set the value.
Set objWMIService = GetObject("winmgmts://./root/microsoftiisv2")
Set nodes = objWMIService.InstancesOf("IISWebVirtualDirSetting")
for each item in nodes
WScript.Echo item.Properties_("Name").Value
WScript.Echo item.Properties_("HttpExpires").Value
'item.Properties_("HttpExpires").Value = ""
'item.Put_
next
Kanwal