Pre-defining the description field of property value groups

Hi,
I am wondering whether it is possible to pre-define the description field of a property value group using PVMT. Using the language of PVMT, when an Extension is made, this essentially becomes the property value group. As you add properties as a child of the extension, you are defining which properties are intended to live inside of this extension/property value group.
As the Extensions are being built in PVMT, are we able to somehow pre-define the description field of the property value group that these extensions are going to make?
Thanks.