The password stored in the Sysprep XML file is not hashed. The string you see there is simply the unicode string encoded in Base64 and can easily be decoded using any web page or Powershell.
http://blog.compower.org/2013/08/05/recover-the-non-plain-password-from-your-unattend-xml/
(Example copied from page referenced above)
Copy the string after and past it in a file (pwd.txt) for
example and copy it to your local machine with full Windows and
Powershell. Then you can recover the password by doing the following:
PS>$encryptedpwd = get-content C:\temp\pwd.txt
PS>$encryptedpwd
VABoAGkAcwAgAG4AbwB0ACAAbQB5ACAAcgBlAGEAbAAgAFAAYQBzAHMAdwAwAHIAZAA=
PS>[System.Text.Encoding]::Unicode.GetString([System.Convert]::FromBase64String($encryptedpwd))
This not my real Passw0rd
The following page (again from the prior link) provides further details on working with Base64 string using powershell, and could be used as a starting point to figure out how to directly encode said passwords yourself:
http://tfl09.blogspot.nl/2013/02/working-with-base64-strings-in.html
That said, as it's not hashed or encrypted in any way, there's no real security benefit to doing so.