When using versioning in Provisioning services the mount option disappears from the context menu. However, you can still mount the VHD from the command line using the following command.
cvhdmount.exe
The executable can be found in C:\Program Files\Citrix\Provisioning Services and is simple to use. Using /? will show you the usage examples, the examples do not show the .avhd format when using version but it works just the same. Just remember, only mount private disk images and DO NOT mount images that are already in use, finally don’t forgot to use the -u command to unmount the disk when you are finished. I would always recommend taking a backup before edit any images.