This thread shows you how to edit the registry
Beta: WM5 ROM editing tool - xda-developers
You basically have to convert default.hv to a text file, make your changes, and convert back to a .hv file.
A few things to remember:
File needs to be saved as unicode.
Paths need to be double back-slashed, e.g. "\\Windows\\Start Menu".
Need to have "REGEDIT4" as the first line.
Values need to be indented by 2 spaces.
The final line needs to be a blank line.